Things I look for when people are having cutting problems:
- Extend your index finger along the front of the rotary cutter, instead of wrapping it around the handle with the rest of your fingers. This helps prevent wobbling, and makes it easier to follow the ruler edge.
- Only cut next to the hand holding the ruler. Line up your ruler, then press it down with your fingertips near the bottom, where you will start your cut ("tent" your hand). If you have big enough hands, keeping your pinkie on the fabric can help. Cut to about the top of your fingers, then move your thumb up to where your fingers had been, and move your fingers further up. Cut to your fingertips again, re-position your hand again. I usually re-position my ruler-holding hand twice when I'm cutting fabric folded once (~22" wide).
- I cut using the lines on my ruler. I know that they are slightly different than the lines on my mat. Do whichever you like, but be consistent. Triple-check that both ends of the ruler are lined up properly before cutting.
- Make sure your table is the right height for you. This will be about the same height as your ironing board. I can't cut at my kitchen table; it's too low when I'm standing, and too high when I'm sitting. I got an adjustable-height table, and it has both improved my cutting and made my back and shoulders hurt a lot less.
- Make sure your blade is sharp!! You have to push harder with a dull blade, and that makes it more likely you will veer away from the ruler, or push the ruler out of alignment.