If you’re a rising senior, it is extremely important to make getting letters of recommendation a top priority. How many will you need? Whom should you ask and when? What should they say about you?

Typically most large public institutions don’t require any letters. Admissions decisions are based on students’ grades, standardized test scores, essays, and extracurricular activities. But for most private colleges and universities, you’ll likely need one to three. The more selective the college, the more letters you’ll need.

Here are 7 excellent tips if they are required:

1. Your school (or guidance) counselor will write your primary letter of recommendation. It should provide your class rank, your rigor of curriculum compared to classmates, and an evaluation of several criteria about you: your academic achievement, extracurricular accomplishments, and personal character.

2. Submit the required number of recommendation letters (or plus one). If a college asks for three letters, then submit three (or, at most, four). Admissions officers can get a sense of how terrific you are with just a few.

3. Try to ask teachers who know you best (and in upper-year courses). You want teachers to evaluate who you are as you head into college. But if you’ve had a teacher more than once, then they are a great resource too.

4. Request letters from teachers in academic subjects that match your interests. If you are considering a major in engineering, request at least one letter from a science or math teacher. And, if you’re undecided but leaning towards a particular major, it’s wise to ask teachers in those areas.

5. Provide your letter writers with a resume and paragraph of your academic interests and achievements. Even if they know you well, they will be writing lots of other letters, so they might need some reminders about your character and what you want to study (and why).

6. Timing: If you’ve requested them before the school year ended, terrific—but be sure to follow up when you return to school. If you haven’t yet, send an e-mail over the summer or right away in the fall. You certainly don’t want to hold up your applications.

7. Say thanks with a hand-written note! Many students forget to recognize their appreciation.