A good triceps program will include a few different exercises for this muscle group while predominately focusing on compound lifts so you can get the most bang for your buck. Since this muscle group works with a variety of other muscles during various lifts, it is really quite possible to do an entire full body workout and include your triceps program right in with it.
Two very good exercises to included in a triceps program are the bench press and the shoulder press. The bench press will really target the chest muscle and the shoulder press will target the shoulder muscle; however, your arm muscles will also play a very important role in executing these movements as well. Therefore, if both movements are included in the plan, there is not a lot of need to perform a great deal of isolated work.
If you did want to do some isolated work, good exercises to look into would be kickbacks and cable pull-downs. When performing cable pull-downs it is very critical that you keep your elbows tight to the sides of the body at all times and really focus on just using this specific muscle. It is quite easy to get carried away and start using the latissimus muscle as well, so ensure that you do not do this.
If you are including both major lifts as stated, then one additional isolated exercise performed for 2-3 sets should be plenty to get this muscle responding. If you are choosing to work your arm muscles in a separate session from your chest and shoulders, then you likely would want to do two or three specific exercises with this part and include between three and four sets per exercise. Note however that this set-up would be one for someone who really wants to dial in on this muscle group and bring out extreme definition. For most people a better plan would be on developing more muscle mass in the arm and that is better served with the compound lifts.