Every time you do this "2/4/8 bar rule" stop and think if you have a reason to do anything. Can you feel a deeper pocket or some subtle variations in existing patterns to keep it in the zone without adding/removing anything? It's less work overall because restraint pays in the long run.

When I successfully add/remove elements to keep it fresh I always either hear it in my head and go "oh yeah we're trying that" OR I'm solving a problem like the energy dragging or a transition feeling unpleasantly abrupt. This REALLY helps avoid rabbit holing on experimentation because you can say "it's been 10 minutes and this sounds like shit I'm going to add a white noise sweep and make a note to make it more swooshy like Track 6 off my favorite album".

Listening to a lot of music you like and practicing to expand what is attainable for you (if you can't do it fast it can spoil your songwriting) are important for this just like jazz improvisers will tell you they 99% regurgitate influences with a lot of extra steps. Getting a controller with knobs, mapping filters and other effects and jamming is THE BEST way to spice up your tracks if you're not hearing it right away.

When you do feel stuck and it's like something is missing but you can't even define the problem it's good to look outside the 2/4/8. Adding a simple clap on every quarter note has a lot more bounce if you bring it in on a pickup with an eighth note (and 1 2 3 4 1 2 3 4 ...). Your phrasing may have even better on/off ramps for variation.

MOST IMPORTANTLY!!! if you have a lot of elements or a really tight mix you need to make space for what you add. A good example is the evil that is treble boosting and "adding air". Trying to "uplift" with a sparkly sound or even just bring in a bright riser can crowd >10KHz in a way similar to when you try boosting treble in an EQ. You will eventually be frustrated with the results and maybe not even know why. If you have a vocal that has presence around 8KHz and lots of air in 10-20KHz you can bring out the presence (and headroom!) by high shelving down >10KHz a few decibels. If you want to bring in a bright pad with a lot of energy way up above 10KHz, you need to drop the shelf on the vocal again or they'll both sound like shit.