Can You Help Me Improve My Stinky Plotting Skills?

I'm in a poor-me mood. 

My plotting skills stink.  I can always come up with a really good idea for a novel.  Then I come up with a couple of sub-plots to weave throughout the story--they're usually threads based on character or emotion.

What I need is help figuring out how to create other plot aspects that branch out from the main plot.  Oh, and that enhance the main plot, that are interesting, and that aren't stupid.

That about covers it. 

Except for my disclaimer that I've never had problems plotting blog articles, magazine articles, my newspaper column, or insurance texts.  Just so you know...

Got any advice?