Keep up Hot Shot and Lead Shot as much as possible.
Use Wildfire every time it's available, Rapid Fire I personally use right beside it.

It's not exactly simple, and yes there is a little RNG involved, but:
Split Shot = 1, Slug Shot = 2, Clean Shot = 3: 1-2-1-3-2-3
If you use Reload before it, the entire shot combo is guaranteed. If Reload comes off cooldown anywhere in the 1-2-3 rotation, you can transition into it. If by chance you need to refresh your Hot Shot/Lead Shot, you can use Quick Reload to force the 2 or 3 proc. Even without Reload, there is a chance for the entire combo to proc. Weave buffs in between shots as they're available.

If you're willing to take that chance, with or without Reloads, there is a chance to literally go 1-2-1- then 3-2-1-2-3-2. . . repeatedly stacking the procs for Slug and Clean. Crazy, yes. Complicated, at times. And guaranteed your luck will eventually run out, but I wouldn't say it if I hadn't tried it and seen some rather satisfying results with it.

You asked for simple, and I apologize for that.