A taller brace height will:
1. Increase draw weight
2. Decrease arrow speed
3. Soften the dynamic spine of the arrow
A shorter brace height will:
1. Decrease draw weight
2. Increase arrow speed
3. Stiffen the dynamic spine of the arrow
Find out what brace height you are happy with by testing your bow at various brace heights. Check your riser and limb manufacturers user manual to find out what brace heights they recommend.
Amend your brace height by adding or removing twists to/from your bow string.
Measure your brace height by using a bow square. Place the bow square at the throat position of your handle on your riser (the thinnest part of your grip) and read the measurement shown on the bow square where the string meets the bow square.