Choose a chart that you feel comfortable with. This is especially important if you are a beginner! There is no shame in starting small!
Never stitch when overtired, especially if you are working with threads similar in colour! Much better to go to bed and sleep, then unpick half your stitching in the morning!
Never stitch when eating chocolates! Or any other food!
Don't fret about mistakes. Unless it's a major one (eg. the wrong colour on a face) most mistakes can be left alone. You are entitled to artistic license, afterall!
Never stitch while engrossed in a good movie or TV show - not unless you like having your work stitched to your skirt!
On the same note, never EVER stitch while watching cricket or footy - not unless you're prepared to crawl around on the floor looking for your needle and threads that all went flying when you leapt up in glee over that run/goal that was scored!