One of the best ways to strengthen your biceps without using weights is doing pullups. Just to give you a goal to shoot for, one of the tests that the military conducts to determine a person’s fitness level is pullups. For a fit man, the goal is 18 pullups. For women, 7 pullups.
If you aren’t able to do that many pullups, it’s time to train. The best way to increase your pullup strength is to simply do a lot of pullups. I’m talking about every day. Don’t worry about over training. You won’t be able to do all that many in one session anyway.
If you hit a plateau, consider adding weights. Just get something heavy and hold it between your legs or use a backpack and put books in it. You should be able to do at least 12 without needing to add any weights.
Once you can do at least 15 pullups, you can start trying out other things such as muscle ups, levers and other calisthenic moves. Just to give you some more motivation, check out these videos:
Apparently, the playground isn’t just for kids anymore.
Doing push ups with elbows at your sides and seated dips (all you need is a chair) will help a lot to build your triceps. Keep in mind that your triceps take up more space than your biceps so if you want your arms to look big, don’t just focus on biceps like most people do.