Wipe away any dirt clumps or anything else on the vinyl. If the vinyl has chunks of stuff on it, the cutter will bog down and most likely create an uneven cut. Use a mixture of soap and water if you cannot brush away the buildup with your hand.
Remove any buildup on the cutting blade. This will ensure that the blade cuts straight.
Feed the vinyl evenly into the machine. Take your time and make sure that the vinyl is flush up against the feeder.
Press the "Feed" button. The vinyl feeds into the cutter. If the piece if extremely long, hold the back of it so that it is fed evenly into the cutter.