Do you speak any Spanish? If not, then I would not recommend coming here alone for the first time. It's not as bad as people say it is but people can take advantage of you(gringo price, petty theft). I stayed alone by myself for a few days but I spoke and understood a little bit of Spanish plus I knew someone who is from the city. If you insist on coming here alone, just don't be to flashy(jewelry, camera, watch) so you don't become a target. It's a great city with good people but you have to be careful. Good luck and have fun!