1) Fighting the Hoard
Most people tend to wait around for the monsters to come to them, usually causing them to be encircled at later levels, and isn't a good way to get XP quickly. You always want to be in a place where you can always damage the monsters effectively. This can be done with a few different techniques.
2) Drilling
Drilling is where you actively move towards the enemies using directional attacks(Speeding Arrows, Lasers, Eggs, etc). This is used when to get a lot of XP quickly early game, and to escape from encirclement late game. Below is an example of drilling early game.
3) Aiming
Aiming is a technique used with drilling to keep moving while staying safe. Blooket prioritizes mouse input for movement and keyboard input for attack direction. By using both at the same time, you can have your attacks go in a direction that isn't directly in front of you. Below is a video of what aiming looks like.
4) Circling
Circling is a technique that when done correctly, damages opponents while keeping you from encirclement. It's just as the name implies, you move around the main hoard of enemies in one direction while using attacks that target the enemies(Acorns, Shells, etc). If you don't have any targeting attacks, you can also use aiming to damage the monsters. Below is a video of poorly done circling.
5) Avoid Bosses
Bosses are a waste of time to try and kill. Bosses only give you 10XP(Red Slime gives 3), but take more than 10x the amount of time necessary to simply kill 10 normal monsters. The only time you might want to kill a boss is on clocktower, where the final 2 bosses have difficult bullet patterns to deal with.
6) Don't use Dark Energy
Dark energy is only good very early in the game when it can one shot slimes and bats. It has one job of damaging enemies that touch it, and it does it so slowly that it might as well be a snail. It damages enemies once and then has a cooldown of around a second, which is a long time. If you really want a protective attack, you can either use Juggling Spheres or Horseshoes.
That's about it for things I can say.