Useful advices:
You should do the reservation in time, to assure good housing.
Change your money in the Airport or in Foreign exchange offices (CADECAS), or banks. Never in the street.
It is better to come to Cuba with Euros or another currency accepted in foreign exchange offices than with American Dollar (USD), as there is a discount of 20 % with the dollar.
You should not lodge at a particular house that is not legally authorized.
Never go with persons you meet in the street, because they might want to take advantage of you.
Take a taxi from the airport (government taxi) directly to the house where you have your reservation, the owners will be waiting for your arrival.
Bring a copy of your passport, because if the original one gets lost you will have to do a lot of paper work at your embassy.
Only buy alcoholic drinks in shops, coffee-houses and bars with a legal licence..
You can change some of your money to Cuban pesos (1 x 24) if you want to cook yourself. There are a lot of vegetables and fruits in the agricultural (farming) markets, generally they are of good quality and quite cheap.
The running water is of good quality, but it is adviseble to buy drinking water.