There are a few things that you absolutely have know and practice in order to compete at the record pace.

The first thing is getting very good at timing your shotgun jumps. in order to do this you need to jump and shoot your shotgun/sniper rifle at the same time to thrust yourself in any direction.

The next thing you need to get good at is building general structures like bridges and towers. To build an efficient bridge out of wood blocks, you need to make the first 2 blocks in length to be 3 blocks tall, the next 2 blocks in length needs to be 2 blocks tall, and the last 3 blocks in length need to be one block tall. this should result in a 7 block long bridge that looks ready to collapse, off of this you should be more than able to cross the chasm or jump to your next floating island.

Speaking of floating islands, you may have some trouble getting to your first one with only wood blocks. well it's actually quite easy. start by placing a 3 block long start, above this do the same thing, so it's 2 blocks tall, 3 blocks wide. For the next 2 blocks in height make them 2 blocks wide, once you have this you can make a 1 block wide tower 7 blocks tall, this should be plenty to get onto your first floating island.

One more thing to get good at and abuse as much as possible is quicksaving. you can quicksave by pressing f5 and quickload by pressing f8. Using this you can quicksave before killing an enemy and if it does not give you the drop you desire, you can quickload over and over until it does. this can save several minutes throughout the run, though you cannot use it at night, as you can't save at night.