There is nothing more important to do if you are trying to find a migraine preventive medication than talk to your doctor. After all, they are the professionals here and so they are going to be able to talk with you about your migraine condition and how serious it is, and what the best methods of migraine headache treatment are going to be in your case.
You should never just start taking any random migraine preventive medication just because you head that it was good and that it worked well. Everyone is different and is going to respond differently depending on the medication so you are going to have to find one that is going to work well with you.
For the prescription medications, there is a reason that you have to talk to your doctor and get a prescription for the drug, and this is mainly because there can be some serious side effects, especially if you have allergies, and in that case they are going to have to make extra sure that you are taking only a migraine preventive medication that is not going to cause you any harm.
No matter what migraine preventive medication they decide to put a person on, they need to realize that this is not a good long term solution. Instead, you are going to have to make sure that you are willing to work at finding the cause of your migraines, so that you can deal with the problem at the source, rather than just taking a migraine preventive medication which is just going to cover up the symptoms and not really do anything to solve the actual problem here.
To find the migraine cause you are going to need to learn about the different most common possibilities, and then find one that relates to your life. For instance if you drink a lot you should know that excessive alcohol drinking often results in migraines, and so you are going to want to stop or at least slow down with your drinking. There is a difference between a migraine and a hangover and people who drink too much can actually experience migraines even when they are not drunk and not having a hangover.
There are various other possible migraine causes, so take some time and find out what the cause is. You can take medication in the meantime to help you find relief but do not stay on for more than a couple weeks.