Getting used to knowing how to take advantage of your Post 9/11 GI Bill takes some time. There are a lot of different factors, depending on where and when you want to go to school. An important thing to remember is to apply for the benefits early. You need to let the VA know that you are interested in taking advantage of your benefits as early as possible.
When I was about a year from separating, I applied here: https://www.gibill.va.gov/apply-for-benefits/application/. By doing it before I got out, it ensured that I received my certificate of eligibility by the time I was ready to go to school. Though they are getting faster, it took one year and two months for me to get my certificate. If you don't apply until you get out, you could be waiting a while to start receiving benefits, and this is really going to hurt if you are depending on the BAH that the bill provides to full-time students.
Another thing to keep in mind, especially if you are in an expensive school area like I am in New York, is to see if the school you want to attend participates in the Yellow Ribbon Program. This is really great, because it will help you to afford the more expensive institutions. For example, in New York, the maximum rate that VA will pay out per semester for tuition is a little more than $12,000. I go to NYU, which is around $16,000 a semester. Luckily, NYU is a Yellow Ribbon School, and they pitch in an extra $3,000 scholarship so that the majority of my costs are paid for. Each state has different maximums and every school (even different schools within a school) have different add-on amounts, so it is best to do your research.
When you finally get to the school you want to go to, just keep in good contact with whoever is responsible for GI Bill accounts at the bursar's office. Get your Certificate of Eligibility to them as quickly as possible and let them know each semester as soon as you register for classes. Sometimes GI Bill can take a while to pay the school, so you need the bursar to know that they will eventually get their money. This way they can financially clear you, and you won't have to worry about your classes being dropped due to no payment being received. Additionally, if you are taking extra loans, the school won't pay you until they are paid, so it behooves you to give them a call every once and a while to make sure they were paid.
Send me a message if you have any questions about the Post 9/11 GI Bill. I try to stay on top of it so I never have any problems.