As a Tibet tourist , you need to keep healthy for the first. Otherwise the high altitude sickness may influence your wonderful vacation. But don't be too worried about it, the Diamox, Nifedipine, Nuodikang Capsules, and Suoluomabao Capsules (known as Hongjingtian Capsules in Chinese) may help some people prevent the occurrence of acute altitude sickness.
Before your Tibet traveling, you have to prepare some permits, like Chinese Visa, Tibet travel permit. Then you'd better to find a professional agency and get a suitable travel plan.
I think you must visit two place. One is Lhasa City, and another is Mount Everest. You can learn a lot of knowledge about Buddhist culture here. At the last, have a good time!