Remember that your TRICEPS make up 3/5 of the muscles in your upper arm so if you are looking to add girth and tighten your shirt sleaves for babes you need to be doing more than "curls for the girls."

You also don't want to focus strictly on your biceps because you risk creating a muscular imbalance which can lead to strength regression or joint injury (elbow, shoulder and wrist).
I don't know if you already put what type of split you are doing but the recommendation someone put above about doing a dedicated arm day is sound, especially if you allow adequate rest from them getting taxed during compund exercises and as long as the rest of your body is progressing well.
Perhaps try a split similar to this:
Monday -- Chest/Triceps/Shoulders -- perhaps only one Tri isolation exercise and let them get hit on the compound chest and shoulder work.
Tuesday -- Back/Biceps/Abs -- same note as above for the biceps.
Wednesday -- Rest (or Legs)
Thursday -- Legs (or Rest if not on Wed)
Friday -- Triceps/Biceps
Saturday -- Abs
Sunday -- Rest (or Legs if you are hardcore

)
For your dedicated arms day try these routines:
FOR STRENGTH: (Sets X Reps/Reps/Reps)
BB Curl
4 X 4/4/6/8
Close-Grip Smith Machine Bench
4 X 4/4/6/8
Smith Machine Drag Curl
4 X 4/4/6/8 --
at Smith Machine bar touching your body, curl up keeping the bar in contact with your body the whole time. Elbows will move back removing the capability of cheating with your shoulders.
Seated Overhead Cable Extension
4 X 4/4/6/8
Hammer Curl
4 X 4/4/6/8
Straight Bar Pressdown
4 X 4/4/6/8
FOR MASS:
BB Curl
4 X 6/8/10/12
Lying Tricep BB Extensions
4 X 6/8/10/12
Preacher Curl
4 X 6/8/10/12
Bench Dips (w/weight)
4 X 6/8/10/12
Incline DB Curl
4 X 8/8/10/12
Close-Grip Bench Press
4 X 6/8/10/12
High Cable Curl
3 X 8/10/12 --
at a double cable station, upper arms parallel to the floor, curl in toward your shoulders.
Straight-Bar Pressdown
3 X 8/10/12
I've had nice progress with the mass routine and plan on alternating the two. You can also extract either the tricep or bicep exercises and do them alone...I just combined them as a "push/pull" type workout.
One last thing to keep in mind...as your delts, pecs, and lats develop, your arms (from head on) may appear skinnier when in fact they have actually grown and your delts are just popping out more thus creating the illusion that they are "skinny." I felt the same way until my wife said "Your guns are getting bigger." :jump1: