As a continuation of the January 15th post,
1) Measure Square: Take the (extra) time to make sure your pieces are cut to the exact measurements. If it isn't started right, it certainly will not end right! When you lay your ruler down make sure you always line up your fabric to one side of the lines. I'd recommend always using the right side. You'd rather have a touch extra, that a touch short.
2) Make Square: Every single time you get the opportunity to square up a piece do it. Yes, you can eyeball it and "think" it is perfectly square. Many patterns require a 7/8" measurements. It is nearly impossible to eyeball 1/8 inch. It may seem tedious, boring and time consuming... it is. There is a reason the designer notes the finished unit size. It's to make your life easier.
3) Be Square: If you take the time to sliver trim each step and every other opportunity in between, when the project is finished it will be pretty nearly perfectly square! It's much more difficult to square up a queen sized quilt than hundreds of 1" x 2" flying geese!
Simply remember: Measure Square, Make Square, Be Square!