I agree with everything that's been said so far. I will highly recommend the use of starch! I don't think it can be over emphasized enough. I use Sta-Flo brand liquid starch and I use a 50/50 starch/water mix. You may want to be heavier on the starch if you're cutting small units.
I also think using the same ruler throughout your quilt is critical. Granted, we usually need different sizes/configurations of rulers throughout a quilt so make sure they are all of the same brand at least.
It may also help you to use a small piece of painters tape on your ruler when cutting. This will help ensure that you are cutting each unit the same size vs on strip 'on' the line; one 'before'; one 'after' the line.
Lastly, relax. As everyone else has said, unless your goal is competition quilting, continue with what you are doing and enjoy the process.
Good luck.