Find some really ugly fabric and learn on that. Is there a particular problem you want to overcome - sliding ruler for example (this can be fixed with Invisigrip-a clear self sticking - with the help of static - on the bottom of your ruler). So, if there is a particular issue(s), tackle them one at a time. Remember, always buy enough fabric for a project so that you will have enough of each color needed in case of a mis-cut...and any mis-cuts that occur just mean you might have to buy more fabric...aw shucks :lol:
See, no pressure there. I took a class years ago when I started. Any basic "how to quilt" class should cover rotary basics. Or maybe you have an experienced rotary cutting friend you know or in a guild who can help. Good luck.