After a hard workout, performing a good triceps stretch is a smart plan because these are a smaller muscle and can become sore quite easily. If you are suffering from DOMS for this muscle and have, say, a chest workout coming up the next day you might find that that workout will suffer as you indirectly use this muscle group as well during chest exercises. A better plan would be to perform both muscle groups on the same day but not everyone chooses to do that so including a triceps stretch is the next best option.
One very good triceps stretch to perform is done by placing one hand above your head. Then bend at the elbow and take your free hand and gently press back on the elbow so the arm moves behind you more. Note that you will likely also feel a good stretch in the shoulder area while doing this as well. Remember to take deep breathes and to also keep the back straight and in alignment.
Another way you can stretch this muscle, along with the shoulders once again, is to find a place where there is a bar that is about neck level. Stand just in front of the bar and then bring arms up, bending at the elbows so the hands can reach behind you and grasp the bar. This will usually work best if you use an overhand grip. Once in this position, slowly lean forward slightly, using your body weight to pull away from the bar so you feel some tension in the back of the arms. Hold for thirty seconds and then let the muscles relax before performing it again.
Taking an extra five minutes at the end of your workout to perform either of these two movements will definitely be well worth your effort and you will be happy you did come your next workout session when you are pain free.