Read the Pattern.
Probably the single most important piece of advice I can give to a beginner is Read the Pattern. Read through it first before you ever pick up hook & yarn. I’m not saying you have to read every line of direction in the pattern, but at least the Notes, Abbreviations, & Materials section as well as any Special Stitches pages that may explain something new you’ve never tried before. Reading through will then give you the opportunity to go check out YouTube for anything you didn’t understand in the Pattern. Same goes for YouTube — watch the video all the way through once before picking up your hook & yarn.