Here's what I can tell you about thinking about using rudder (and this is very rudimentary, and not EXACTLY how it works, but it'll put you into the mindset):
Think of using the rudder as making a left or right turn on a flat plane. Like, if you were in a car, and you turned left or right, that's how it would turn, right? Well, that's kind of how rudder does it. The aileron ROLLS the plane, so if you were looking out of the cockpit and you gave it a bit of left on the aileron stick, the left wing would drop and it would turn left, in a bit of a roll. Do a hard left, and it'll do a barrel roll.
What I would suggest for practicing it is just take it up a bit where there's no trees or anything, and give it a bit of left or right on the rudder. Just see how it turns. Don't go hard left or hard right; you just want a little bit to see how it interacts. If you just give a little bit of stick and the thing is turning violently to the left or right, you may need to put some expo into it.
Just do some simple, easy turns at first; feel it out and see how it reacts, so you know you can recover from it. Maybe spend a battery just trying simple, easy, large circle turns. Once you have a feel for it, start trying harder, full stick turns so you know what it'll do. Then put a little bit of aileron in and rudder (but not much, because you'll find it will turn pretty sharp when doing both, and it might be uncontrollable if you're not expecting it). Again, just kind of get the feel of it.
Rudder is, I think, more of a "feel" than the bank n' yank that many pilots fly with. I managed to jump into it fairly quickly for fixed wing flying, but that was because I started with a racing quad and then went to a plane - don't do that LOL. My opinion (and again, just an opinion) is that putting in a mix is detrimental, and doesn't really teach you how to turn with the rudder, so I suggest trying it without.