David Gernon, now a senior at Northwestern University, where he is pursuing a BS in economics and a BA in journalism, reflects on a pivotal period in his life in a letter to his younger self.

Dear David,

Your last semester of high school definitely had its ups (prom, getting an A in comparative literature) and downs (losing in the first round of the state tennis championships, missing the flight to tour Northwestern, and cracking another iPhone). Sure, you had fun, but if you knew what I know now, I bet you would have done a few things differently.

Actually Study for AP Exams

Heads up: College classes are expensive. Seeing lots of your college classmates graduate a quarter or two early will make you realize earning college credit in high school can be a really good idea, especially in terms of getting value for your money. If you had studied a little (or, in some cases, a lot) harder for those AP exams and earned 4s or 5s (equivalent to Bs or As at most colleges, respectively), you could have saved as much as $6,000. I know senioritis makes it hard to study, but taking the long view in this situation is definitely worth it.

Learn to Cook

After living on your own for a few years, you’ll know exactly how good it feels to have a home-cooked meal. Unfortunately, that’s tough to make happen when you don’t live at home and don’t have the slightest idea how to cook anything very interesting. I mostly stick to sandwiches, spaghetti and soup. It gets old fast. Hit up Mom — she’s a world-class cook — for some lessons during these last few months at home. It’ll make college life a lot more satisfying.

Write Teachers Thank-You Cards

You were perfectly happy to get to know several of your teachers well during your high school career. Your journalism teacher, especially, inspired you to apply to and attend the journalism school at Northwestern University, a decision that continues to bring you joy and satisfaction today. Go ahead and tell her this. Go beyond a casual “thanks” on the last day of class and take the time to write a note. It’s simple: Notes last longer and mean so much more.

Plan for Summer

Graduation means seniors finish school early, and your college’s late start date (thank you, quarter system) will leave you with more time than you know what to do with. Be more on top of your game. Don’t set yourself up for a summer of literally laying around. Instead, plan activities with friends and family, walk your dogs (you’ll miss them when you leave) and make some serious progress on your reading list. It is one of the last unstructured summers of your life. Take advantage of it!

Do these four things and your last semester of high school will markedly improve. Oh, and don’t forget a Sharpie on the last day of high school to sign those yearbooks!