Scopes , Health Meters , Compass' , and other HUD stuff is fairly easy. I learned from reading the guide on Health Meters and the Grenade making guide.
Next Download a scope mod and take them apart , play with them until you understand how it works.
If you can understand how it works in the first place then you will feel alot better about the mods you make.
There are two Guides here at AA that togather , should help you to understand how they work.....
http://www.alliedassault.com/community/guides/hobbs/
http://www.alliedassault.com/community/guides/warpig/
Dont expect not to have to work for it , TriggerHappy. I think even the best Modders here will agree with me , it takes time and alot of trial and error.