When push-ups are mentioned, first thing that comes to mind is probably chest training. Push ups are primarily a chest exercise, but with a little modification they can become a very good exercise for your arms and shoulders.
Regular pushups do work your arms to a lesser degree, but push up variants such as the biceps push up or the diamond pushup target your triceps and biceps more.
Do these two exercises 2 to 3 times a week to build your arms.
Diamond Push Ups
1. Place your hands shoulder-width apart on the floor. Drop to your knees or support yourself on your toes. Bring your right hand in 3-5 inches toward your left hand. Bring your left hand in 3-5 inches toward your right hand to do inside pushups.
Now your hands should be about 2 inches apart. Diamond pushups will hit your triceps harder.
2. Straighten your spine and tuck your hips. Your torso should be parallel to the floor with your arms perpendicular to your shoulders. Squeeze your abs to stabilize your torso.
3. Rotate your elbows so that they are pointing toward your feet. Bend your arms and lower yourself toward the floor. Keep your elbows pointing backward so they brush your sides as you go down.
4. Press your arms straight again and raise your body up again. Do 20 to 40 push-ups, rest for a minute, and then do a second set.
Push ups with Biceps Emphasis
1. Get in a regular push up position. Your legs should be straight and you should support yourself on your toes.
2. Point your hand fingers outwards to an angle of about 45 degrees.
3. Lower yourself while squeezing your biceps and come back up. Exhale on your way up.
Source: Fitness and Power