This might sound vague, but here goes anyway.....
I always start with a mental image and a scrap of fabric. It usually get's ugly from there...... I hack away with sissors and make lots of small unrecognizable scraps. Generally speaking I shelve about 90% of my ideas for future trial and error.
Every once in a while I get lucky.
The main thing is -- DON'T BE AFRAID TO TRY TO DO SOMETHING use your mind and let your heart get involved and if at first you don't succeed, then keep trying.