some random suggestions:
pin the pieces together
starch the fabric really well
don't chain piece. I rush alot when I chain piece and tend to get sloppy so take it slow
mark your sewing lines (some people just sew straight across)
recheck your measurements and try sewing the scant 1/4 inch seam.
Also, don't "iron." Just "press" and don't use steam. Steam distorts the fabric