Ann Logan

Set up your main stitching station so that you are comfortable and avoid injury. If you don't have the luxury of a specific place to stitch, chose your perch carefully. Don't sit in an awkward position. Your seating should allow you to work freely, with your arms in a natural stitching position.

I assume that you yourself understand this, but still I will say. It is very important to wash your hands before touching the fabric or thread. Of course, you are going to wash the finished cross stitch design, but why make it dirtier?
In case you use a thread or fabric that is hand-dyed wash them in advance so that they do not stain your handwork.
Unwind your thread from time to time. Just leave the needle and let the thread loose - it will unwind itself... Or help it a little to unwind.
Do this every few stitches, otherwise the texture will be uneven and the fabric will show through your stitches too much.