Tibet will come to its best season from August, less rain and mild weather. But please pay attention to the great temperature difference during day and night.

hello,
august in tibetan region may be like the spring time in other parts of china. autumn is always the best time to travel

but if u r foreigner, u r prihibited travel independently in tibetan region, u gotta find a local agency to help get the tibetan tour permit from the tibetan govern. and u must travel with at least one guide all ur trip when u r in tibet! so when u go there u may find an agency from whom u can rent a SUV car, dirver who most of the time is also the guide. private travel with a guide is not bad, if u come there for the first time.i have been there once with a private guide who have become a friend of mine, if u need help, u can drop me line.