The Tenderloin is not a great place to get lost so take cabs to avoid accidentally wandering around here. It borders Union Square on 5th, so its easy to wander the wrong way.
Unique Suggestions: However, if you're feeling adventurous, try Thai Noodle at 901 Larkin. You can get a beer and lunch for under $10 and it rocks.
Fun Alternatives: Or, if you're vegetarian, try Golden Era Vegetarian Restaurant at 572 O'Farrell.
SF is a city with lots of slopes. If you shot pictures near a slope, please make sure to hold your camera properly. Otherwise, you will get a photo of SF after earthquake. See the sample of my photos.
Driving in San Francisco can be very tricky. There are alot of extremely steep hills, one-way streets, and scary intersections. If you are planning to drive there for the first time, be sure are familiar with the street system.
The Castro District is suppose to be the gay area of San Francisco, but I have not been there. There used to be a red light district near Broadway and Montgomery, but I don't think there is much there now.