I'm left-handed too, and cut thousands of yards of fabric for our store. I use a left-hand Martelli Ergo cutter, and the blades last for months and months.
The key I think is to cut the fabric, not the ruler. The cutter should be perfectly upright, not tilted back and forth or side to side. The side of the cutter should contact the ruler slightly but not put a lot of pressure on it. It's really a matter of practice and lots of it. Cutting straight and not at an angle will also make your mats last a lot longer.
The difference in being left handed is really not strange; just work from the left side of the fabric instead of the right, and work on the left side of the ruler instead of the right. You may have to learn to count backwards if your ruler is not smart enough to do both. :mrgreen: Lots of cutters have reversible features, Martelli ergo cutters come in left and right-hand versions. Hope this helps.
Oh ya, and never cut toward yourself, that's a recipe for ruined fabric. All that blood on your fabric is hard to get out. :shock: