I been to Havana now 2 times, the first time I went there I had problem finding cheap accommodation online, in the end I booked a package Holiday, which was not really what I wanted a a little bit expensive, I wanted a cheap place to stay and be able to find my own way, possibly travel around other parts of Cuba, and just use Havana as a base.
My secomd trip was more successful, I booked my accommodation online with Hostels247.com Check them out, they have quite a few places in Havana to choose from http://www.hostels247.com/HAVANA/ I stayed at Marthas Guest House Havana.
Another cool thing about Havana is a lot of these Hostels and Guesthouses are family run, in most cases the families still live in the same house, if you can find one, this is the best way to get to know the real Havana.
Other cool place to visit in Cuba are Varadero, Santiago de Cuba and Santa Clara. Just travel around and get the feel of the country.
Cubans are really friendly and still have one of the unspoilt minds, they will go out of their way to help.
One thing to bear in mind when travelling to Havana or any other part of Cuba is, Cuba doesn’t have the usual western shops and fast food restaurants, I don’t concider this to be a downfall, the purpose of going to new places is to see the way other people live and to gain experience of new cultures. I don’t think Cuba has much of holiday horror stories, just keep your wits about you and have fun.