Craftsy has a new class that's on sale right now for $14.99 by Debbie Caffrey: 'Cut to it: strategies for smarter quilting'. It's a great class that addresses among other things, this very issue ~ not w product but w a couple of unique and well-explained hand positions.
I'm a lifelong quilter/sewist and learned ALOT from this class. It's one I highly recommend to everyone.

I use my ruler with a "Quilter's Slide Lock" tool. Works perfectly every time. I have the long one and the short one.
A friend told me about them. I have always been rotary cutting challenged! The website is: quiltersslidelock.com

I put the little sandpaper dots under my 6x24 ruler. It gives it alittle grab. Tho accuquilt is having a sale so I kinda got a bonus and ordered the 1 1/2 strip die, the snowflake die, and the 8 inch circle. I had already gotten the 2 1/2 inch strip cutter, these should be good for alot. I wanted the 1 1/2 inch so i could try the log cabin blocks, my sister wanted the snowflakes and we got the circle for a jeans quilt.

I put that rubbery shelf liner under my ruler. It has really helped me and it doesn't slip anymore.

I use the June Taylor Shape Cut too. I use it for everything. Otherwise I simply can't cut straight.

Dina

In addition to the other suggestions which I agree with, putting the clear Invisigrip nonSlip film on my long rulers helped a lot.

The trick to cutting without getting that V is to line the fold of the fabric on a line on your mat, then cut absolutely perpendicular to the fold. If you get a V in your fabric, it's because your angle is off.

...in addition to all of the above......as you are cutting, your spread fingers on that ruler should be parallel to your rotary cutter...so you place your spider-leg like fingers down with good pressure onto the ruler, cut just pasted your fingers, stop, but leaving rotary cutter in fabric,reposition your fingers to uncut area and continue cut.....takes longer to write this and sounds more convoluted than it is, but doing it is smooth and pretty much foolproof....becomes automatic over time...

I use a 6.5 x 24.5 inch ruler. I have clear rubber dots on each corner of the ruler and one mid-way down on each side. Also, I have found that if I re-straighten the cut side of the fabric every 3 or 4 strips, I don't get the curves and v's. Also, I try not to have more than 1 fold in the fabric. I have friends who will fold their fabric 2, 3 times and cut. When I have done this, the thickness causes problems and my ruler can move off like more easily. So I try not to do this unless I really have to.

Can I get an AMEN on that!!!! Love mine.