use tile sheets
don't overuse 'every tick'
is key down vs on key pressed
the computer is constantly checking whether or not the key is down, so that takes a little more effort then on key pressed.
the same goes for similar events checking whether a condition is true or false.
using higher resolution sprites or a lot of animation frames can slow ya down a bit.
gigantic layouts take more effort as well.
particles and webgl effects can slow ya down as well.
try to space out the demands you place on the computer where possible.
in general just bear in mind, that the more you ask the computer to do the longer it will take.