Measure your blocks after every seam and make sure that you have true 1/4 inch seams.
Check that when you are pressing, you are not distorting your blocks or maybe not pressing them all of the way open.
Do not use steam when pressing, either.
Start off sewing on a scrap of material and butt your block up next to that, it helps get an accurate seam allowance at the beginning of your seam.
I'm sure you will get more hints/help too :wink: