1- Decide if you want a restored car or one that needs work. This will be a huge part of your decision. A restored car may sometimes cost much less than what it would cost you to restore one yourself, not to mention the difficulty you may have in finding available parts. However, if you are doing the restoring yourself then you may save some money.
2- Join online Forums and ask many Questions. Before you decide the model, do a lot of research and figure out what kind of problems each car may have. Luckily, there are plenty of websites and online discussion forums for classic car enthusiasts to get info.
3- Attend car shows and talk to others who own the model of car you may want. Again ask many questions, especially from those that own or have owned the type of car you are looking for.
4- Have a vehicle appraiser look at the car. They may be able to tell if it has been in an accident, or if the engine, transmission and other vital components are not original. This will alter the value of the vehicle.
5- Check history of the car. Check DMV records and find out how many prior owners a car has had. Find out how many accidents it has been in and what sort of problems it has had. If they have any repair records this would be a plus.