How can I get my MInecraft Mods to work?

my minecraft mods wont work. its 1.6.4 mods and im using 1.6.4. i have all files in the right place, i might just need to back up the minecraft.jar file, but i dont know how to do that. and that might not be it. so please list anything and everything you can think of and ill try it and see if it works. also, i did delete meta-inf. please help me! i want my minecraft mods back!!