Stuff i wish i'd known when i started weightlifting.
Do not buy commercially available training magazines. eg men's fitness, flex etc.
Do not mess about with bodypart splits, isolation exercises, cables, etc. Keep it simple to start off with.
Do not try to progress too quickly. Slow and steady is better.
Do start with a broad foundation. Full body workouts with squats, deadlifts, bench, dips, pull ups, military presses. Big compound exercises.
Do eat a healthy diet. No need to fuss on specifics, just good quality non-processed food.
If you're unaccustomed to lifting, then for the first few months start of slowly. Tendon strength lags behind muscle strength and prgressing too quickly could lead to injuries.
In fact if i could go right back, i would spend my first few months doing only pushups, dips, all pullups/chinups, and deadlifts.