First Rule of Quilting: there ARE no stinkin' rules!
ignore anybody who says "you must".
that being said, there are certain practices that will more often give better results than others. picking fabrics that work well together is one. i don't care how much or how little you pay for a fabric. if it doesn't work and play well with the others in your quilt, you are going to have a rough time putting it together.
i'm not among those who object to polyester. there are certain things i've noticed, though, whenever i work with it.
- needles wear out faster, and smaller sizes (11 or less) work better
- it doesn't always feed as smoothly under the presser foot
- it won't always be able to tolerate the highest iron settings like cotton can, so test it first
- i don't like to prewash. i'm too lazy. however, if i'm planning to use a combination of fabric types, i do prewash to make sure everything is preshrunk before i start sewing things to each other.
- i don't like to pre-press, either. also because i'm lazy. but i always get better results if i do. that's proven true even when all the fabrics are 100% cotton, but from different lines or manufacturers. ironically, it's the more expensive stuff that's more often temperamental. go figure.
when i bought all my fabric from the same place, i never encountered "issues". but now that i've started branching out and shopping online, too, my world is more uncertain. i'm trying to get into the habit of cutting test strips to wash, press, sew together, etc before i start the real work.