Some days, I’m doing effing amazing. But often there are days where I can’t do crap, and I don’t know what I can do so I can be more consistently good, other than “practicing.” How do other people deal with this?
Watch yourself play, the only way you’re gonna get more consistent is to be able to understand the mistakes you make.
Record the games esp the losses and you’ll see these times when you’re like oh duh I totally was out of position etc. Over time you can get better at not doing those things
That’s a good idea. Also, one thing in particular that bothers me, is that my aim is often super inconsistent 
Playing on low dpi/sens helps with aiming.
Consistently play, try to pay attention to everything going on. You’ll notice your own and enemy players tendencies after a while.
Watching back your games is good advice. Wait until you see yourself play once you are just watching the game. Usually watching you make mistakes is enough to correct some of the big ones.
For sense?
Really just make sure you can do a 180 turn in a mouse swipe. Typically run higher sense on non critical aim heros.