I keep the mojo going by always having something to look forward to. My basic rules:
1/ Never do more than one model at a time. This means you can also look forward to the next build and want to finish the one you are working on. That is specially true when you start researching the next build when just over half way through the previous one. So I will look up schemes on-line and order aftermarket for it but cannot start until I finish what I am working on.
2/ Have a small stash. This both gives you something to focus on and look forward to without being distracted by too many options. I never let my stash go above 10 and want to bring it down to 5.
3/ Read on-line reviews and watch YouTube videos of new products and kits. Try to always have some new tool/paint/material you want to try out on the next build.
4/ Look at the builds and conversations being held on here.... there is always something to inspire.
5/ Don't overdo it. Limit your time at the bench. You can look forward to an hour or so most days leaving you keen to move the build along at the next opportunity. If you end up spending hour upon hour in a session it becomes a bit of a chore. Even on days where I am left alone I will still limit my time on the bench in favour of a good film, a book or a session in the pub.
6/ If at all possible have an area dedicated to modelling. That means you can just leave it and return to it without putting things away or clearing up. I remember in the old days, the thought of getting everything out on the kitchen table, or the tray, and then having to put it all away did not exactly encourage me to persist.
7/ Finally - this is personal, I like a tidy clean work area and it is always more inviting to sit down and build when it is tidy. Consequently I do work in a fairly tidy manner and don't leave a mess behind. In a way that contradicts item 6 but not really, it is all a matter of degree. Bits of your model around the bench, a craft knife and sanding stick or two to pick up and use, is different to hardly being able to see the bench through the accumulated detrius. I also do a 'deep clean' of the work area, airbrushes, brushes and tools between projects. It takes about 3 hours or two to 3 sessions to get things ready for the next build.....
That all works for me....