My cutting has improved since I started putting several dabs of clear "rubber cement" on the backs of my rulers so
they don't slip. Works much better for me than using those suck-on handles or the peel & stick non-slip clear backings. When they begin to wear off, just reapply new dabs (you can remove them anytime by just rolling your finger over the edges & they roll up & off).
Also, the June Tailor Shape Cut is great for getting straight cuts. My only regret about it is that I bought the 12" one instead of the larger one. It's been worth the $$ for me as it eliminates 'elbows' in long strips. Since I bought the smaller one, I often have to fold the fabric a time or two before cutting, in which case I use a 60mm rotary cutter to cut through the four layers more easily than with a 45mm blade; easier on my hands.