just make red ball go faster

but for real, here's a guide:

First, make sure you're using the IGT edition, which can be found in the Hack Collection in the Resources page linked under Guides on the left.

Once you're in level 1, when you start the run, make sure you get a green timer on the bottom left, indicating that you started moving on the first frame possible. If the timer is black, that means your start wasn't optimal, so your end time won't be optimal. There's a few easy ways to do this. You can hold R to constantly restart before you press right/D, which is simple and works most of the time. Alternatively, if you're using Windows, you can also hold the right mouse button over the game window bar above the game, where the Minimize and Close buttons can be found. Then, drag your mouse cursor into the game, press R, hold right/D, and let go of the right mouse button. This will guarantee an optimal start, though sometimes you'll need to move your mouse cursor to unfreeze the game.

Next, you'll want to jump at a specific spot that will make Red Ball go slightly faster. You want to tap the jump button at around when the right edge of Red Ball's body lines up with the end of the word Right above you. If you do this right, Red Ball will be traveling 3.125% faster than normal for the duration of the jump, which is enough to save a frame. After this, if you manage to do the jump over the wall without hitting it, you'll get a 3.097s run. You can tell if your timing is off by looking at the end time: if you get 3.129s, your jump was probably either too late or a frame early. If you get a time above 3.129s, your jump was probably too early. You can also tell if you jumped early by seeing if Red Ball fails to clear the gap without losing speed.

So how do you get a 3.065s run? It's pretty simple. Simply do the same thing as above, but hold the left button (or A, if you prefer) for exactly two frames (or around 0.065 seconds) as Red Ball is falling towards the ground from the first jump, and make sure that you hold both right and jump as you land from the first jump. This allows Red Ball to maintain a slightly higher speed than normal throughout the second jump, which is enough to save another frame. The timing on when you hold left for two frames is very lenient, so focus on getting the first jump and holding left for the correct number of frames. Make sure that you aren't holding right while pressing left, or the trick won't work. Practically, you're going to just be tapping the left button to do the two frame left press. If you get this two frame left press along with a good first jump and a jump over the wall, you will likely get a 3.065s run, which is world record. Sometimes, you will get the 2 frame left press but not get 3.065s anyway due to how Red Ball can land from the first jump, but with enough tries (and maybe slight adjustment of how high the first jump is), you'll get the 3.065s world record run.

tl;dr: to get 3.097s, start optimally, jump at the right spot, do another jump cleanly over the wall to get 3.065s, start optimally, jump at the right spot, tap left while falling, do the jump over the wall