Do legs! You are an idiot if you don't. Even if you throw them in by just doing free weight squats / one legged squats or lunges holding, like, a 10 lb. bar bell or whatever, you will never thank yourself more. Don't use the squat cage or whatever if it was giving you pain before but ignoring your legs actually LEADS to injury more than to it. Plus then you don't have chicken legs compared to the beach muscles you're flexin' up top. It's a great way to avoid IT band problems as well as issues with shins/knees that plague anyone. Also, warm up for one mile, cool down for a half or just run 8-12 minutes and then cool down by walking around a track if there's one at your gym or nearby for like 15 min (avg time it takes to walk a mile.) Legs are just as crucial as the often ignored back extensions, (which you should also be doing randomly mixed in 3 days a week with your ab routine that you better be doing to finish off 'cause if you don't you're an idiot x2.) Like anyone said, stay away from machines, always use free weights and bars and vary your routine from month to month. Do hammer curls as opposed to just curls for bi's for example or switch from bar curls to free weights and vice versa. Don't do arms together and tri's are totally a days worth if you are doing it right, none of those other things will work it enough, and it will help you RIP your chest up and get great gains in bench, skull crushers or whatever else you're doing for chest.
Set your routine now because you will realize no goals at all if you're just randomly throwing yourself at machines and weights doing what you think is right. Isolate your target muscles and hit them hard on their day. Cycle in some rest here and there and get as MUCH protein as possible, an old adage would be 1g for every lb you weigh, although that's not science. Eat ground turkey, chicken breasts and egg whites if you're able or chard and, I think, kale if you're veggie, although there're great sites out there for protein rich veg diets, I can not hang with them though.
Also, if you're serious, cut pretty much any drinking down to the weekends exclusively and learn to say absolutely, positively NO to empty foods and drinks. White bread, soda, candy and sweets blah blah blah, all just absolute horse shit for anyone dedicated. This includes almost every possible meal you can buy on the go as well, so pack your tuna sandwiches accordingly. It doesn't mean you shouldn't treat yourself once in a while but don't do it with a cheeseburger, make it worth it by having your mom make you delicious homemade cookies or something else you will actually appreciate. Also, drink water every chance you get, as much as possible, doi.
Do all this and you will see results in NO TIME, like 2 months or so and you're set. You'll also notice that your cravings, because your body will stop responding to the impulse eating you were doing for however long before you started, for sugar and such will pretty much drop off the map. A side note, everyone knows it's bad but corn sugars also make your brain quit responding to being full, so their sinister purpose is really just to make you eat and eat and eat, it's like if they put Chinese food in everything.
I used to be a workout freak, so that's that, but I don't live it so religiously anymore. Check this site:
http://www.bodybuilding.com/ to get into it, free routines, exercises and advice is rampant there and it's really quality stuff.