Great question - My major challenge has been going from a "creative spark" to finished product.
My approach differs according to the genre...
If singer/songwriter then : Pat Pattison's method taught at Coursera (https://www.coursera.org/learn/songwriting
) is damn useful. (P.s. it's a free course and quite brilliant!) The concept of boxes - one of a host of tools he shares during the course is a powerful one.
If metal/rock/blues/jazz then it's usually a guitar riff/progression that I want to work into a track. Record the rif/progression, loop jam drums and bass till I find something that works and build up the track as we go along. If lyrics are needed I'll use a few of Pat's tools and try ideas over the music. The last two things I usually track in are lyrics and solos.
If other (electronic music/ambient) then I probably have been inspired by a sample or drum loop. For the the more upbeat stuff I mess around with starts from the drums, then bass line. The ambient stuff is usually a guitar/bass riff worked into something.
More often than not - the methods will overlap - sometime you have to write something specific and that where Pat's tools comes in real useful. The december challenge (xmas carols) was a good example : had a melodic idea (lyrics), worked some chords and then developed lyrics to fit. A bit of a iterative process, but was fun!