There are many nationally recognized certification companies that you can go through to become certified such as ACE, NASM, and AFAA. Some require attending classes while others allow study at home or online. Do some research to find which company is going to best suit your needs and career goals. If you want to train a very specific demographic like a collegiate soccer team, you may need a different certification than a trainer who wants to work with the average client wanting to live a healthier life. Once you receive your certification, plan out what you want your continuing education credits to be according to your goals. If you want to open your own personal training business in the future, the classes you take will differ from a trainer who wants to have only pre-natal and post-natal clients. Usually you have to update your certification every two years, so aim to take classes every 6-9 months to avoid having to take a class you don't care about at the last minute, keep your knowledge up-to-date and show your clients that you are proactive in the fitness industry.