I take a long time to finish my paintings, and it's difficult for me to keep the same mood throughout a painting. So, to have the same feel throughout the piece, I make a cd of music of the same mood for each piece, and listen to that cd on repeat. It really helps me create a cohesive feel.
As for coming up with ideas, I am always thinking about what to paint, and ofen frustrated that I am not thinking of somthing good enough. I take lots of digital pictures for photo reference, and I look through the internet for image ideas. My expriences, emotions, and thoughts lead me to pick certain images over others, and I use those to spark painting ideas.
Here's a fun engine for that, btw:
100 Random Pictures:
http://www.ga2so.com/random2.php