Nothing can prepare you for the excitement that is Havana.
You just have to go and emerse yourself in the cultural tidal wave that will overpower your every sense. Like everywhere else in the world you need to exercise some common sense when out and about. Remember that this is essentially a third world country ,the people are just trying to survive and you are a millionaire in comparison to them. That aside you'll find them warm and engaging and nothing is too much trouble.
If I could give one tip thats maybe not in the guide books its to get yourselves lost. Its the best way to see the city. If you wander around with your nose in a guide book your going to miss more than you see. Yes you should walk the Malecon at sunset, but not all of it, it goes for miles, better to come off it at irregular intervals and nip into the back streets and then back on to a different part. Yes go for a cocktail at The National Hotel, but dont spend all night there its full of tourists, dont eat in the hotels, the Paladares are excellent, great food great company and great value, also you know the money is going to the family NOT A COMPANY. The best one we found was called Lilliam's , its near the Sealife Centre in Miramar and all the hotels and taxi drivers know it. NB You have to book its very popular especially at weekends. Taxi's at night travel everywhere by taxi and get it from either your hotel or a hotel near where ever you end up. DO NOT HAIL ONE IN THE STREET.
The city orientation tours are good but in the main the tours to the cigar and rum factories are vastly over rated.