These are some tips I've picked up from some well respected Audio Directors over the years. They're fairly basic and simple, relatively subtle, and a matter of taste. But I'm a big fan of doing things like these to make my sounds feel more cohesive and smooth to the ear.
Here's an example of something I put together which I was really happy with at the time, design wise. I like how it sounds, it syncs well, and has some interesting layers:
Three years ago I would've been good to go with a sound sequence like this. And for most people it's probably fine. But the me from today hears a lot of jagged edges, a trickle of frequencies that jump out of line, and some harsh highs that pop out, especially on the "cocking elbow" bit in the middle.
Here's the same sequence after some compression and EQ thrown in:
This is how some compression can come in handy. Used to taste, it can "tuck in" some of those edges that are popping out of line, smoothing everything out evenly, helping to glue together all these layers so that they feel more like one weapon transforming, instead of a bunch of junk thrown together. After the waveform has been smoothed out a bit, then I like to shelve out some of the highs, depending on the source material, to "warm" it all up a bit. In this piece, there's some somewhat shrill elements at the beginning, and especially when he cocks his elbow that I like to pull back with the shelf. Here's a shot of the FX I used:
It's worth mentioning that this is not a universal, catch all process. It's a case by case basis, and I apply processing like this only when the piece asks for it, which to my ears, this piece did. At first, the version without processing might sound more enticing, mostly because it's louder, but to my ears it's a bit of a mess. The processed version, to me, sounds much smoother, cleaner, less piercing in the high end, and like it belongs together. Put simply, more cinematic. The unprocessed version has a lot of high frequencies that stand out too much, the biggest culprit being the elbow coking part, which flies right out of the speakers way too aggressively (and can be spotted in the compression screenshot, right in the middle).
I'd like to reiterate that a lot of what I'm saying can be a matter of taste. Just be mindful of any shrill high end frequencies in your work, and try to make your layers glue together to seem more cohesive.
I hope that was helpful to someone, and if you have any questions or comments, feel free to email me!