Rhonda

Since I start out with the cut down method I don't generally check each block unless one is obviously not the same as the rest but I do measure a lot along the way.
I pay particular attention to the corners(blocks and 4 patches etc all along the way) being square. If you are sewing along an edge that is not straight your seam will be off at the end where the block might have a bit of a flare to it or is too short etc. This is usually the first mistake that starts the whole thing rolling and when you look back you will see that it was crooked to begin with. I also make sure all along the way that the edges of each section is square and trim or fix it if it isn't before I add any more. If you fix your seams from the start so they are straight and square you will prevent a lot of frustration in the end.

I guess I could have added this also.

I don't sew in rows. Rows can get distorted. I sew into 4 patches and then sew two 4 patches together and then sew those 8 patches together. If you sew sections together rather than in rows you have a better chance of keeping things in a square shape. When you sew in rows it is like laying tile. Every small measurement that is off will be magnified by the time you get to the end of the row.
If you sew in sections you can see right away if something is cockeyed because your 4 patch won't look squared up. So you will know to fix it now rather than get to the end and see a row that looks like a wiggling snake. Use a ruler to see if it is straight. Measure measure measure!!
Prevents a lot of problems!! But remember NOTHING IS PERFECT! You notice I did not say noone is perfect!. That patchwork is just a thing! Not your identity as a quilter. It is a lesson in the road of quilting life. So enjoy the jouney! The bad teaches us a lesson and the good lifts our spirits so ENJOY it! Don't stress! Walk away and come back later if it is getting to you.