I write most of my songs directly onto the DAW. Whenever I have an idea or a melody (it's usually short, just 4 bars), I write it into the DAW and extend from that instead of laying out the track's entire arrangement. I need to change that.
I noticed lots of good tracks have good compositions and arrangement. I'm also more fluent with melodies rather than drums, so most of the time, my drums are just basic ones, which I think needs to be changed.
Oh, also! When ever I have a melody in mind, I find a BPM tapper (whether it's online on desktop or an app on my phone), and try to tap out the BPM of that melody. It's a start for most of my drafts.
Just gotta find what works best for you. I like to start at 7am. Which could help explain why i am not in a band, who wants to wake up deink coffee and start writing? As far as the bars go i lime to just do 4 bar parts even though i count in threes. But if all you have is 4 bars just save it in a folder with the tempo listed. If nothing else you can come back to or just try and fit in with another tune your stuck on. Just list tempo and key ... it will help.