The best way to get better at grammar is to read, read, read. Any kind of books you like. Almost all have been professionally edited, at least for spelling and punctuation. Liberties are sometimes taken because we don’t all speak like textbooks. Reading immerses you in language and works far faster and better (at least for me) than learning grammar rules by rote. But do remember that your grammar won’t improve overnight, so don’t get stressed if it takes you a bit of time. Getting college paper help from your peers or teachers will also enhance your writing skills.