Advice on developing ideas?

Hello! 

I'm looking for some advice on how to go about developing a single idea into an entire piece. I've always had trouble with this, and in the past my solution has been to tie different ideas together. But this would usually result in the piece sounding choppy, rather than one smooth piece of music. Creating that sense of fluidity is the biggest thing I've been struggling with recently, and it's been keeping me from being able to progress on any of my ideas. So I was wondering, how do you guys go about expanding on a single idea? And how do you go about creating smooth transitions between separate ideas? Any advice at all would be greatly appreciated.

Thank you!

The previous thread has some good  ideas on this already.  The main this is use your source material and don't deviate