A prerequisite to sewing clothing for yourself, is being able to take your measurements accurately, but we are often left to our own devices to figure out how to do this properly. Or, worse, we simply buy the pattern size we think we are, and then are unhappy with the resulting fit.
Good sewing habits make for happy sewing time. You know the old saying 'a bad workman blames his tools', well unless your machine has a problem and is in need of some TLC from a sewing machine mechanic, the problems generally result from your end! Get into these good habits and avoid some frustration.