Just do exactly what you do normally. All shot preparation and execution as you would do indoors, with the added step of tilting your aim upwards after drawing.
Bend at the waist, pushing hip forwards. Don’t lean back or bend your back knee, it just gives more room for variation and inconsistency.
Initially, use a normal bowsight to find where you should aim horizontally. In sighters, shoot pairs of arrows at various heights. Each pair should be aimed at a point in the scenery that you can come back to later. You can then use the distance between the pairs, distance from arrows to the target and the distance between points you aimed at to extrapolate where you should aim to hit the target. Once you know that, you just need to match up some point on your bow to a point in the scenery that allows you to aim in the right place.
Aim using a definite point on your bow at a definite point in the scenery. Find a point on your bow like the inside corner of your arrow shelf, and use it to aim at a definite point in the scenery like a particular leaf on a tree. Don’t aim at some distance along a line or between two points, aim at a point.
Don’t use your knuckles, they are round (not a point) and subject to variation between shots. I always use the corner made between the shelf of my riser and the arrow, sometimes with a marked piece of tape along the far edge of the shelf if I need to adjust left/right. However, with a weaker poundage bow you may need to use lower parts of the riser such as corners of side rods.
If you use your V-bar/side-rods, make sure they stay perfectly horizontal and don’t tilt either way!
Use a foot marker. Very important. Since the point you aim at is probably further away than the target, the parallax effect resulting from any movement along the shooting line will change where your arrows go. Don’t rely on the positions of other archers to find your own position; use a definite foot marker like a target pin stuck in the ground.
For more information including the scoring procedures and rules on sights see the following excellent presentation from the ArcheryGB Judges Committee: