First up, I've just gone over 25,000 words on my novel! It's been a long time coming (the several month 'break' didn't help), but I'm happy nonetheless.
Secondly, planning. Usually, when I begin a new piece of work, I follow the same routine:
1. Come up with an idea and jot it down, generally in 30 words or less if possible.
2. Leave it for a few days. If it still sounds good, continue to step 3, otherwise, get rid.
3. Write a basic plan, create a character or two to suit, and decide when and where to set it.
4. Begin writing the story and, 5 minutes later, realise that nothing I've written resembles the plan in any way.
5. Rewrite the plan to suit the story I have just written... Seriously.
The strange thing is, if I just start to write with no plan whatsoever, I get stuck pretty quickly. If I have a plan I don't, even if I don't follow it!