Curls, curls, and more curls...ie, preacher curls, dumbell curls, with a straight bar, with a curling bar, standing and seated. Add close grip lat pulls, close grip seated rows ect. While your at it, work on the triceps, a big group of muscles that respond well to heavy use. Well developed biceps look good but the the triceps give your arms the mass. Oh, and work on the deltoids to round out your look. Honestly, if you want to weight train, a full body workout would be best.