I start with sound design, because that's what drives my tracks more than things like genres and tempos.
I usually have a kind of vague plan like "today I'm gonna mess with this thing for the drums, then put that synth on top... and see where that takes me"
Having too much of a defined idea at this stage only works against you because you'll ignore sounds with a lot of potential, just not the one you're looking for.
I just keep messing about until I have something, a sound or group of sounds that really grab my ear. Usually it comes from the interaction between one or more sounds,
an instrument and it's effect chain, or finding a technique I know I can apply to other elements in my track. Having that makes me relatively sure that I have a bunch of ways available to modulate and change for variation.
My experience is that you need that interaction... if you start building from 1 nice sound and 1 nice drumloop, you still have to figure out a progression for them. I've been producing beats for well over a decade now, I know the ledge, but working like that still will put me up against a wall with not many ways to get over it.
So look for sounds that interact with each other in an interesting way before you get to the composing stage is a real tip. Once you have an idea going like that, it'll usually inform the rest of the creative decisions, like what rhythm or tempo, what sounds to add (if anything.. if it's a good idea it'll probably work best with a lot of flourish), etc. Since I figured this out I've hardly been stuck on any tracks anymore, there are better and worse ones obviously but I've never been stuck for inspiration. So if I have the time to sit down for it, pay it attention, then yeah.. I can be really fucking fast and keep up a constant output.
Another real simple tip that helps a lot: Stay varied. Never do anything half-assed, make every move and decision count.. but at the same time always make sure to have a bunch of different things going on. Different projects, or similar ones in different stages. If you're stuck for inspiration on one project, move to the other.