My son started having night terrors when he was about 18mos. He had 2 or 3 almost every night for close to 12 weeks. I took him to our Dr. and researched night terrors on-line. If they are happening regularly, pay attention to what time he starts crying. What you can do is, distrupt his sleep 20 to 30 mins prior to him having a night terror. This should change the pattern of his sleep cycle and hopefully avoid the night terror from occuring. If you are getting up anyway to console him, it isn't that much different to set your alarm and go in to prevent it from happening. To disrupt his sleep would be to rub his back or roll him over. Don't wake him up. Just stir him enough that it changes his sleep pattern. Do this for 4 to 5 nights and, hopefully, you will have caused a new pattern of sleep without the night terrors. I did this for my son, and they were the only 5 nights he didn't have night terrors. Unfortunately it didn't work for me in setting a new pattern, but it may work for you. My Dr. said in 6 to 12 weeks a new pattern occurs anyway.
On-line I found 3 other tips... Some kids are stimulated by a night time bath. So, I now bathe my son in the morning. A cool room is better than a warm room in preventing night terros. Lastly, what others have mentioned, it is very important for these kids to get all the sleep they need. My son is almost 3 now and still has them occasionally. If he hasn't had enough sleep, I can pretty much plan on him being up in the night. Hope this helps!