Master the proper form on bench press, pullups, deadlifts and squats and make these four the staples of your workout. Before you get into different routines, approaches, etc., build up a base level of strength by doing lots of compound exercises (exercises that require multiple joint movements like bench, incline press, deadlifts, squats, front squats, pullups, chinups, rows, cleans, and lunges. Don’t bother with curls, leg curls, leg extensions, leg presses, flys, or tricep press downs for now).
For some people, overhead pressing can be difficult on the shoulders, so work on scapular mobility and rotator cuff strength before you get into a lot of overhead presses and stay light when you do start overhead stuff. Work on hip, knee and ankle mobility as well. Shoulder, knee, hip and ankle mobility is way more important than you’ll realize until you hurt something due to a lack of mobility somewhere. The source of an injury many times originates from somewhere other than the location of pain, so prioritze mobility and flexibility everywhere.
Use a light weight that you can comfortably perform ten or more reps with so that you can groove the proper form for these compound moves with some resistance. As you become more comfortable with the right form and have built up your muscle memory, slowly start adding weight. If you go too hard too quickly, you won’t learn the right form/technique and you’ll become injured or become acclimated to the wrong technique.
Since you’re a beginner, you’ll probably see a significant amount of improvements very quickly regardless of how hard you go, so get the form right first. Compound movements, because they involve more than one joint and therefore more than one muscle (hips and knees or shoulders and elbows), will allow you to use more weight than an isolation movement (you can bench more than you can do flys with, you can squat more than you do leg curls or leg extensions with). Your arms will develop strength with these moves anyways (pulling works biceps and pushing/pressing works triceps) so devote your time to the big movers to reach a strength level where you can start to use significantly heavy weights if you choose to incorporate isolation moves later on.
Also, work on grip strength as much as you can. Deadlifts, bent over rows, even pullups and chinups require a certain amount of grip strength and if this breaks down before the muscles you are targeting do, that set will not be as effective as it could be. Wrist curls, squeezing stuff, holding heavy ass barbells or dumbbells for extended time can all help this. Good luck. Oh, yeah. Eat right and eat more.