sole visitor 1st time to tibet , need best advise.

There are many attractive spots, such as Barkhor Street, Jokhang Temple, Potala Palace, Sera Monastery and Norbulingka are some of the must seeing places there.
Gang-gyan Hotel is very good and you can have a try.
I think for only one visitor, the best transportation is the taxi. The price is very cheap to take taxi there.
As for the clothes, I advise you to take some long sleeved clothes, which can protect you from the sunshine.
You need to take enough cash and your credit card.
As for the food, it is hard to tell which to avoid and it depends on you.
I need to remind you that, you need to have a Tibet Travel Permit, othewise you can do nothing.