i always know what i want the beginning to be like. and the middle. but tying it all up is a pain and i really don't know how. especially for a really long story. any ideas?
List all of your dangling threads. Decide how to tie them off. Make notes. Do it. Simple if not easy, but it does work.
Or for that matter, whether to tie them all off. Life doesn't tie up all loose ends, and modern novels tend not to either. But for each thread, make it a conscious choice.