(On Delta planes at least) The aisle armrest comes up if you press a little trigger underneath near where is meets the seat. Makes it easier to get up if you’re in the aisle seat and to exit the plane.
If you are always hot, get a windows seat. When you’re at altitude, the side of the plane gets cold, so the window seat tends to be cooler.
If you are on the tall side, once the fight attendant isn’t looking anymore, put your backpack or laptop bag behind your legs / knees instead of under the seat. Then you have full legroom available to stretch out.
If the person in front of you reclines their seat back, ask the fight attendant for a pillow and a can of soda. Remove the pillow case, and put the full soda can in it. Then batter up, and bash that fucker right in the face. Just kidding. Don’t do this. Just calm down.