Layer Masks and Blending.

Hey,
Can anyone tell me how to best use layer masks?
How to use difference within a layer mask?
and how in the HECK you make a texture color not completely flood the entire image and make it look retarded? I'm really stuck on this part.
I don't understand how to get
this
and this
to NOT turn into this

or something equally as horrid looking. I want it to just blend nicely and add a bit of color to certain areas without making it shockingly white or extremely dark.

You can also see my horrid results in the pathetic icon I made a while ago.
I desperately need some help! lol