Have a gameplan
A lot of the time when you see people go into the gym they are just going in to do something. Cardio, maybe some curls, a press machine, maybe, maybe a leg press and finish off with something like a tricep pushdown. Now going to the gym is better then not going in terms of your creating some type of stimulus. But actually having a game plan laid out on what you are going to do is going to produce far greater results. Mental preparation for what your about to do is one aspect but laying out what your doing for each day and each session if going to allow you to break up the different muscle groups into appropriate sessions allowing you to properly train and recover in a way that will promote optimal results. Your training split is your gameplan. Your split tells you what areas your targeting, at what frequency, volume, and intensity. In general, If your a beginner who has no existing injuries or significant imbalances(we all have some imbalances) I would recommended doing full body workouts 2-4 times a week. All workouts exclusively full body exercises. Squats, deadlifts, chest press, overhead press, pull ups, dips , etc.(also all exercise modified to fit your experience and comfort level. ex, assisted pullup machine vs normal pull ups). In your beginning stages you will be able to make greater progress by affecting more areas at once because they are new stimuluses. As time goes on you will need to break the body parts up more as you will become more conditioned and it will take a greater effort to create a new stimulus. So maybe instead of a full body workout 2-4 times a week you’ve upgraded to doing a upper/lower split. Training upper one day, lower the next, then off, repeat etc. There is a point of diminishing return though. Going to the gym 7 days a week doing 1 body part a time for a small duration might sound like it could work but again we need our central nervous system(CNS) to rest as well. So in order to make good consistent progress we need to have a split that fits our needs but doesn’t overtax us to the point recovery is hindered.