Working on your triceps (the back of your arm) contributes to having bigger arms as well.
Exercise: Overhead tricep extension.
One of the best exercise to tone/put on mass on your arms.
Aim for 6-8 sets x 8-10 reps.
Watch it on YouTube: https://www.youtube.com/watch?v=pRNni85gItg
Make ARMS look bigger this SUMMER with this exercise!