Here are a couple of things to keep in mind:
- It's way easier to revise than it is to create from scratch.
If you get an idea and are feeling motivated, run with it. If you stop to work on any one section too much, there's a chance you'll lose track of the bigger picture then struggle to come up with other sections. Get a rough outline of what you have in your head, then go back and flesh it out later. If you have any ideas along the way for other things, write them down so you don't forget. If you're in the "arrange/compose" mentality, you should compose and arrange. If you switch to sound design or mixing, it'll be much harder to get back on the composition train. Kinda like how you could concentrate on studies and homework for a while, then check Facebook for two seconds, and then just not want to even look at your homework anymore. Think Newton's First Law of Motion

-Not all aspects of production are equally enjoyable, but all are required for a quality production.
As producers we bear the burden of ALL aspects of a musical product (well, us with integrity anyway). Mixing, for example, is often not going to be as enjoyable as composition or even sound design, but you have to follow through. If you leave a track half finished without mixing, you've only improved in whatever you worked on in the track. You'll make no progress in mixing. Focus on various aspects individually, but make sure at the end of the day you're as well rounded as you can be.
-Same applies to sections in a song.
The breakdown or outro might not be as exciting to work on as the drop or chorus of your track, but they're still important. A great track isn't just a great chorus (though you could get away with that), it's a great intro, breakdown, buildup, etc. If you leave a track 3/4 done you'll miss out on making progress in whatever you left out.
These are just some general tips I like to follow, obviously not universal rules that you NEED to follow. They've worked out for me, and they make sense, so I share. Hope this helped
