One thing I have recently learned is when you cut your pieces, keep them stacked in the direction they were cut. The reason is, fabric has "give" (or stretches) selvage to selvage, but not lengthwise, so if you get them turned around, some blocks will stretch and others will not, so you get mismatched seams. My last checkerboard came out perfect using this info. None of the others have! With triangles, stack them in two piles, upper cuts, and lower cuts, and try to match the stretch directions for both piles with what you are joining them to. I stick a pin down through the "no stretch" edges so I do not mix them up.