Contact moves, e.g. your third move don't work as well on the larger boards. Consider approaching from a distance. Especially with stones on their own.
Avoid creating many small groups that lack eyes. You can easily end up dying everywhere.
was on a key shape point for that eye space but is not going to help you if they can make eyes elsewhere, e.g. here it could make one at A16 for sure and could run down if it needed to because of the E13 stone.Always ask yourself before you atari if them pulling the stone/group out helps them or you more. Sometimes it's best not to atari.
Other than that, always consider if trying to save a group of stones will bring you more trouble than they're worth. If they aren't cutting your opponent's stones into two groups they're probably not that important unless there's only one or two of them. By corollary avoid creating groups of stones that aren't doing much for you.
Others may have more/better pointers. Welcome to the game.
