My previous releases have so far all been collections of tracks I made individually, without much thought about a finished collection.
I generally try to produce tracks that work well on their own, allowing every track be what it wants to be, - often in very different styles. I like the freedom of that, even though it sometimes turns into “shitty experimental tracks” as well:) ha ha!
When I decide to make a demo, I begin by looking through my available (more or less finished) un-released tracks, - taking notes along the way.
…and then start putting together a selection.
I use Ableton’s arrange view for this, often making several different versions, with selections that “go in different directions”.
This can be tedious work, since in order to decide on the best selection of tracks, I have to listen to all that old stufft - over and over - like some dusty old custodian.
Sometimes I’ll mix/fit existing tracks into each-other, like a DJ-set, but mostly I’ll just select tracks that I feel work well with each other, adjusting the timing, individual volumes etc.
I’ll sometimes try to make small custom made “interludes” or special effects for transitions, but usually end up deciding not to use them after all. At this point, I think I could probably make a 20 minute EP composed entirely out of un-used transitions.