If you would like to improve the shape and size of your arm muscles the solution is to work them regularly. Training the arms right will tighten them up, and create more balanced and eye catching shape. How far you go in terms of size development is your call.
If you took a cross section of the upper arm you'd see that the triceps (the back of the arm) makes up about 2/3 of the 'meat' of the arm, the biceps (the front part) only makes up about 1/3 of the arm mass. So it makes sense to spend at least the same amount of time working the triceps as you do the biceps. If you've become obsessed with biceps training start putting more effort into your triceps as well.
The best way to train arms is through resistance exercise with weights or machines. With limited equipment a barbell or some dumbbells are enough to do the job.
If you lift weights regularly you might have recognised that when you do a pulling movement for back (like a row, pull down or chin up) you are also working your biceps. When you do a pushing movement for chest or shoulders (like bench presses or shoulder presses) you work your triceps. So it's important to consider this indirect effect when planning how you'll fit your arm training in. If you don't get the timing right you may end up exercising them too often. Sure, if your focus is purely toning then this may not matter so much, but if you'd like to develop some extra muscle shape or size then you need to get this right.
Trained correctly the biceps and triceps only need 1 to 2 workouts per week, maximum. 2 different exercises for both at each session is also plenty, although if you are pushing for size development then 3 exercises can help. Generally aim for lower rather than higher numbers of repetitions per set as the arm muscles are primarily fast twitch dominant. This means they'll respond better to lower repetition sets with heavier weights. For men this is 6 to 10 reps, women 8 to 12 reps.
Here's a list of some of the better biceps and triceps exercises to choose from. For excellent results include some of these each time you train arms:
- Barbell Curls
- Dumbbell Hammer Curls
- Arnold Concentration Dumbbell Curls
- Seated Incline Bench Dumbbell Curls
- Cable Straight Bar Pushdowns
- Dips Between Benches/Chairs
- Behind Head Dumbbell Extensions
- Close Grip Barbell Bench Presses
For any exercises you don't recognise let me know and I can send you demonstration links to show you how to do them.
Remember, when you're seeking muscle development your body has a greater need for high quality protein and nutrition. It's not all about training. Spend some time on better eating too so your muscles will be well protected and can recover properly.