As others have said, vary your exercises . . . and do something that is weight-bearing (other than just body weight). Also, what kind of gains do you want? Do you want to increase strength and general well-being? Do you want to add mass? Do you want to be cut? Different plans apply to different goals. I personally think the first one is the best and most-important.
One of my favorite "do-at-homes" is with a sandbag. You can purchase a 60lb bag of sand at a local garden center or hardware store for cheap. If you have an old duffle bag with a handle, your possibilities are endless. You can use various increments of weigh - put 5-10lbs in ziplock bags - and pop them in the duffle. You can do curls, front squats, regular squats, dead lifts, Bulgarian dead lifts, and Turkish Get-Ups (my favorites) for a combined cardio and lifting plan. TGUs work EVERY muscle in your body and are great for non-muscle-burning quick cardio.
Diet/nutrition (and a normal sleep schedule) is also VERY important. Make sure you are getting enough protein and managing your micros and macros. Simple carbohydrates - like raw veggies and fruit - are great; complex carbs (like refined sugars) or "empty foods" (like bleached or "refined"/"enriched" wheat flour) are bad. Creatine can help for mass-building and may be purchased on the cheap online - just make sure you are buying unadulterated, pure creatine with no additives from a reliable source - i.e., no "mixes" and not from China or another dubious origin. Creatine should also be in powder form and not in a sports drink - it loses its effectiveness soon after being mixed into liquid. Don't listen to what the wahoos (who are often fatties and have no idea what they are talking about) at health supplement stores say.
Form and not hurting yourself are also very important. If you can afford it, research a good personal trainer and invest in a few sessions. If you cannot, there are some good ones on youtube. Use your douche-dar to make that determination. Likewise, the most aesthetic body types are formed from things people are supposed to be doing - i.e., physical activities like sports, running, cycling, rock climbing, etc. - rather than just gym time. I can't tell you the number of "bros" I see in my gym with weird, disproportionate bodies (think: chicken legs and weird shoulders). I don't know any women who are into that body type . . . or at least quality women. I'm assuming the same goes for dudes who are into dudes. If this isn't the case, mea culpa!
Do routines you enjoy and that make you feel good. Nothing is more anathema to your fitness goals than just working out to "look good." You'll hate it and will soon quit.
Be "smart" about your workout. 30 minutes of effective training will do a LOT more good than 2 hours of ineffective training - you'll actually lose muscle (e.g., if you are doing really high intensity cardio all the time) if you don't plan it right.
Keep a journal and log your workout so that you have a physical record of your improvement - either in reps or weight. It is also an easy way to ensure you actually are mixing things up enough.
If you live near a public park, many (at least in the U.S./Canada, Europe, and Oz) have fitness equipment you can use in the middle of a walk, run, or jog - e.g., a pull-up bar, olympic rings, etc. Don't feel embarrassed to use them - everyone looks like a dork when they do, and, who cares, right?!
Be able to detect broscience BS on forums - like bodybuilding.com - there is a lot of misinformation out there. Fortunately, it is relatively easy to detect. Even for someone who may be new to the game.
Good for you, brotha, for getting serious about your health and fitness. Hope this helps, good luck, and have fun.
