This is how I start - that is once I have thought and thought and thought about a painting project = projects in this case. The thinking it out takes the most time - rolling the thoughts around in my head and pitching them to those I respect for feedback.
Then I make a plan on the process
and then I begin ....
I always start with an INTENTION for the piece - sometimes its a word, a quote or a poem
There always under there even if you don't see the words in the end.