Intro
Hello! There hasn't been a guide on First Debt% in a while, and since I am really into the category at the moment, I'd love to write one myself! Although I have ran the category for a few years, I admittedly am not the best or most consistent runner, so this guide may not be perfect - however, it is the general thoughts I follow when I do my runs.
To start off, here is the general outline of the run! When you start the game, you select your name, town name and town layout. After you talk to Isabelle, you travel with her to the town hall, and then immediately go to Nook's Homes to get a house from Tom Nook. You pick a house as close to the town hall / train station as possible, then run back to the town hall to talk to Isabelle and plant the tree in your town plaza. If you haven't located and picked up a perfect fruit, now is your time to do it, after being free from the tree sequence; once you have the perfect fruit and another regular fruit, you head to Nookling Junction on Main Street, and buy a shovel with the money you earn from selling the two fruits to them. Finally, you go back to town, find the money rock, and go to Nook's Homes, using the money to pay off your first debt.
I'll also say that I've never done this sort of thing before, so if I get anything wrong, please correct me! All of the splits I list are just how I segment the run, you are free to do whatsoever. The time estimates are also the estimates from my PB.
Setup
Before starting a run, there are a few things you need to make sure you have. To my knowledge, the fastest language for this game is KOR / NTSC, and I found a time loss of 1-2 minutes by using English, as that is what I used to run. Since this run is mostly mashing through text, small text improvements really add up. You should make sure your totally legit copy of ACNL is Korean, and it also helps to have a totally legit and Nintendo approved Save Editor so you don't have to go through a lengthy process to reset each save file once it saves at the tree planting. It is also worth knowing what NTR and Snickerstream is if you have no way to stream your 3DS to your PC.
Next, you need to set up your 3DS to have the correct time. Since you need to go to Nook's Homes and Nookling Junction during the run, you need to make sure both are open. Here are the opening/closing times for the shops (they cannot change, as you cannot enact an Ordinance yet):
Nookling Junction: 8:00am - 10:00pm
Nook's Homes: 10:00am - 8:00pm
It's also worth saying that you should avoid any events taking place when you're doing you r run, as an event announcement (such as the Fishing Tourney) wastes a second or two when you are in the town plaza. If all of this is in order, than you should be good to go!
Split 1: Train (~ 1 min)
When you start the run, you begin on the train and set up the save file, giving Rover your character name and town name, as well as selecting the initial layout of your town. The main goal of this split is to just get through it as fast as possible, while selecting a layout that means you have travel the least possible distance to each visited location, just being the town hall and town plaza. Ideally we want the perfect fruit tree to be close-by as well, but the spawn location cannot be controlled, so you just need to hope that it's in an easy to find location when the town is made.
Start the run by spamming through the text - I personally hold down R (which makes the text scroll faster) and spam A, though holding A/B and spamming A/B also works too. When asked for your name, choose a one character name, and same goes with the town name.
This is the general town layout that I look for when starting a run:
The positions of the town hall and town plaza are interchangeable here; we just want both to be as close to the train station as possible. At no point in the run do you travel directly from the town hall to the town plaza, or vice versa, so the distance between them doesn't matter as much.
You can actually ask for another town layout from Rover if you want, and for newcomers I would recommend doing that so you have more chances of getting a layout that is good enough, requiring less resets. However, every time you say no to a layout, it takes around two seconds for Rover to bring up another, so for people going for really low times, a 2 second time loss immediately after starting the run may not be affordable. Rover only comes up with 4 layouts before looping through the same ones again, so after four, either pick one or give up and start another run.
Once you've picked your layout, just spam until you are off the train! I split when the screen goes fully white after talking to Rover. This is around 52 seconds for me, but as this is just text spamming, the time doesn't differ too much.
Split 2: Tree (~ 4 mins)
Once you arrive in town, spam through the text until you are free (the text options for Isabelle don't change anything). At a certain point, Isabelle will show you the map and you will be free. Glance at the map to remind yourself where the town hall is, run there and enter. After spamming through more text, run down whenever you are free to exit, and when you are outside, run directly upwards to the train station, and through to Main Street. Run to your left to Nook's Homes, and talk to Tom Nook. You can spam through this, as the dialogue option doesn't matter, and you will be outside the train station with Nook.
You will be free to move while Nook is running from Main Street slightly behind you. While you can move, you shouldn't - as moving too far from Nook will make him stop you and tell you to slow down, overall wasting time. Wait for him to stop moving (or very slightly beforehand), and run to a place to set up your house, by talking to Nook.
Set up your house as close to the train station as possible, and closer to the town hall if possible, as you will have to run there afterwards. Make sure to be careful of being too close to the train station, town hall, town plaza, any other villager houses or rivers/rocks, as Nook won't let you set up the house, wasting around 5 seconds with his dialogue. If there are any rocks that have space around them, it may be worth risking setting up your house so the rock is two tiles away from any of the tent's borders, for reasons I'll mention later. After the tent is built, run back to the Town Hall when you are free.
This is a good time to look for the perfect fruit if you haven't spotted it, as running from your tent to the town hall may uncover land that you haven't seen yet. When/if you find the perfect fruit (a fruit tree with one of the fruits having a different, usually shinier design), shake the tree by pressing A to make all the fruit fall to the ground. Pick up the golden fruit as well as one of the regular ones - the perfect fruit goes for 480 bells, with the regular ones going for 80 bells, netting you 560 bells, needing 500 to purchase a shovel.
There is a backup strategy for when you can't find the perfect fruit, but I don't usually use it. You can shake two regular trees to get 6 regular fruit, and go into your items menu (by pressing X) and select your character and remove their socks (the top option). With regular fruit going for 80 bells, and the socks going for 32 bells, you end up with 512 bells, just enough for the shovel. Picking up the fruit and removing your socks is time consuming, so I'd only use it if I have no idea where the perfect fruit is late into the run.
(Perfect Peach - credit)
Whether you find the fruit now or not, enter the town hall, and remember to run up to Isabelle. You can spam through her text until she asks for your birthday, where you need to confirm it by using the touch pad, so be ready for that! I've forgotten sometimes. Now you just need to spam through for a minute or so, until the tree ceremony has finished. I split when the villagers start clapping after you plant the sapling. Getting the perfect fruit deviates the split's time around 10 seconds, so if you get the fruit in this split, you will be ten seconds ahead of a run where you get it in the next split - but obviously, it lkevels out after the Shovel split.
Split 3: Shovel (~ 1 min 30 secs)
At the beginning of this split, after spamming through the text and saving, you either have the perfect fruit (+ regular fruit) or you don't. If you don't, follow the guide in the previous split; if you do, or you find the perfect fruit tree, run to Main Street and head slightly left into Nookling Junction.
Go through Timmy/Tommy's text, and run up to them, selecting their first dialogue option to be able to sell your fruit. Sell both of your fruit (or your fruit + socks), and head over to buy the shovel. Spam A, but make sure to press B when I dialogue option appears, as Timmy/Tommy is asking if you need a tutorial for using the shovel, which obviously wastes time.
I split when the screen fades to black after leaving Nookling Junction.
Split 4: First Debt (~ 1 min 30 secs)
After you have bought the shovel, your only goal now is to find the money rock! Run from the Main Street back to town, equip your shovel (quickly, by pressing left/right on the D-Pad), and look for the nearest rock to hit with it. Hitting the rock with your shovel has recoil, pushing you backwards, so after two-three hits you will have to walk forward again. Getting the maximum amount of money from the money rock requires you hitting it 8 times in a row without too much time between each hit, so you have to make sure you cannot move too far away from it while hitting it.
You do this by digging two holes in the positions above, in any corner of the rock (I believe there are other positions that work, but this is what I do). If you built your house (tent) near a rock, or there is a tree in the same position as the holes above, then you may not need to dig two holes. This is ideal, as digging a hole obviously takes time.
Hit the rock eight time. Rather than spamming it, I wait to hit the rock until the money from the previous hit has appeared, as hitting the rock too early may make a delay that ruins the timing. When all the money has been hit out, pick up the last two bags to fall out - you need 10,000 bells to pay off Nook, and the last two bags hold 4k and 8k each, resulting in enough to pay him off.
if the first rock you encounter doesn't work, it's unfortunate but you will have to just keep looking. Once you have the money, all you need to do is run the Nook's Homes! You do not need to unequip your shovel, as entering the building unequips it for you. Spam through Nook's text, run up to him when you're free and talk to him again. Spam through until you are outside, and that's the run finished! Remember that the run ends when you your villager pumps their fist.
Conclusion
Thanks for reading! Hopefully this is helpful. Please let me know if I've got anything wrong, but this is the way that I approach each run.