One thing, If you are going to do a lot of driving and exploring, Remember it is the rainy season. A lot of the roads (especially to the ruins and in the South end of the country) are muddy and have big potholes.

DEFINATELY rent a 4 wheel drive. (you will thank me later) Almost all the rental agencies have them .

When you park, don't leave any valuables, camera's, laptops etc on the seats in plain view.

Watch for dodgy charachters around the ruins. They sometimes hang around there to rob tourists. Just use common sense, be aware of your surroundings, and you will be OK.