I shot competitive archery for 25 years (2 state championships, a five state championship and 17th in the nation at the week long nationals) so have shot uphill and downhill and had to learn what happens.

When you shoot level your bow arm is square to your body and the bow (and arrow) reacts a certain way at the shot. This is how you sight in.

Now when up in a tree most just keep their torso erect and drop their bow arms. The arrow no longer reacts the same way as when the bow arm is level so the arrow goes high (WAY high!).

When practicing keep your bow arm square to your torso and bend at the waist. Now the arrow still might hit high (gravity) but not nearly as pronounced as when you change the relation of your bow arm to your torso by dropping it. Same applies on uphill shots.

Another "trick" is when shooting in the wind most archers move the bow over to try and compensate but their "mind" subconsiously wants to be on the target. When they shoot they don't realize it but move the bow towards the target.

Target archers have "levels" on their sights. Some hunting sights have levels. In a left to right cross wind (example) you "bubble over" the top wheel toward the wind so the bubble moves to the side and aim at the target. Right to left wind bubble over the top wheel to the right and aim at the target. You will hit the target without having to compensate for the winds effect on arrow speed or arrow direction.