An exellent post from K.M Weiland on explanation. One that i found a tad funny, 'cos i can totally tell that i often do this and later when i read over it i'm like, "gah! what are you doing!!!"
The basic tip is to let your readers have the benefit of the doubt, don't go overboard, and let your readers imagine. They don't need everything spelled out.
Hope this helps, or it at least creates a giggle :)