A reticle, such as Mil-Dot, can be used to assist in distance assessing, wind compensation and long range bullet drop compensation.
The most accurate reticle will have one central targeting point with additional points all around it, and the easiest to use have spacing lines measured in miliradians, which is a measurement of the length of an arc and its radius.
Reticles are best when placed in the first focal plane of a riflescope so that the dots will remain 10 cm apart at a 100 meter distance, no matter what.
Miliradians allow you to adjust for bullet drop without adjusting the reticles position and by knowing the size of the object you are targeting, you can also use miliradians to adjust for wind.
Read more: How to use Tactical reticles