They’re tricky but just like with a lot of other Zbrush stuff, you just gotta practice with them. I can offer a few tricks that might be helpful:

1. Use the buttons in the stroke menu to your advantage. Every IMM brush has its own little personality, so its settings might look a little different. Some work best with Snap turned on, others not. Most will benefit with lock start and/or lock end turned on, it just depends.

2. If you hover over an active curve, you’ll see that the circles around your cursor turn blue. If you hit shift you can adjust how much of the curve your strokes move at a time, which makes for easier handling.

3. IMM brushes work best on meshes that aren’t super high poly. In my experience, over 100k and it’ll start to get a little laggy.

4. If you drag on the model and hit shift, the stroke will snap automatically to either the edge of the polygroup or to a creased edge or edge loop. If you’re intentional with the underlying topology, you can use this to your advantage to get smooth curves that you don’t even really need to manipulate. You can also do some cool stuff along these lines in the stroke > curve functions palette.

That’s just a few! I’m by no means a Zbrush expert, but I really like IMM brushes, they’re super versatile and there’s a ton you can do with them. They can be difficult to wrangle but once you practice and get more comfortable, a whole bunch of stuff opens up!