The way to become a lobbyist is to first of all, attain at least a Bachelor's Degree. If you can get a Masters Degree, that is even better and more influencial. That is a must or you cannot qualify to be one. It is a good idea to have your degree in political science, law, economics or a related field.
If you want to be a lobbyist, you will need to be considered an experts on whatever issues you will be working on. You will need to prove that you know your subject matter and that you are a benefit to the cause or you will get nowhere so you must be persuasive as well. You'll need to be a people person too because there are many people you'll be dealing with. It will be helpful for you to be adamant about the things you are lobbying for because if you are not, it will show but if you are passionate about the causes, that will be apparent as well.