How persnickety are you - when it comes to sewing/quilting?
And about what?
Quality of fabric - brand is not important - but how it feels , thread count, and how it washes up is
Grain lines - I have learned to check to see if they are "straight" before buying. If the design is printed off-grain, no amount of tugging or blocking is going to get the design "straight".
Being aware of the print of the fabric. My SIL wanted me to make a dress for her - and she bought exactly amount of fabric shown on the back of the fabric - and the repeats were big and the design was splotchy. I was tempted to put the big yellow flowers right on her boobs and crotch area, but I did try to scatter them "gracefully" . Some prints (on garments, anyway) do not "scatter gracefully"! (I have been entertained by those placements, though.)
Anything that you are "fussy" about?