Let me try to explain my method using two rulers. I butt two long rulers
together (same brand to avoid confusion). I align them on the fold of the
fabric with the bulk to my left. When everything looks straight I make
my first cut by holding the ruler to the right. Remove the piece with the
raw edge that I've trimmed. Now I start cutting my strips. One ruler
stays on the fabric (to the left) and the other ruler moves to the width
of the strip I want to cut. Align both rulers on the fold. Remove ruler
on the right while holding on to the ruler on the left and cut. Hold on
to that ruler until you are sure you've made a complete cut. Make sure
that your rulers have enough grip otherwise it will slide. I use the
Slidelock ruler because I don't have enough strength to hold on to
those long rulers most of the time. I put clear Nexcare tape under
my rulers so they don't slide.
Hope it's clear as mud. ;-)