For better or worse, letters of recommendation are really important for internships, scholarships, and graduate programs.

The good news is that (most) professors see writing letters as part of their job, and are happy to do their part to help you succeed.

The bad news is that you still need to ask several of them to write letters for you, which can be intimidating.

Different letter writers will have different preferences, so always check in with them to see what they need. But here are some ideas for how to plan the process:

• Choose wisely. It's important to have people (generally professors) who can write positive letters of recommendation on your behalf. Generally speaking, it's better to have 'senior' letter writers if possible, but the most important thing is to have at least one (or more) people who know you, and who can speak to your potential as a scientist.
• Start early. Writing a good letter takes some time and thought, and it's to your advantage to give your letter writers that time. A month in advance isn't too soon. Up to a week in advance of a deadline can be OK, though two weeks is certainly better. After that, there's a risk that your writers are either too busy to do something like that on short notice, or they simply may not have time to write something as polished as it should be. Different people have different thresholds for when it's 'too late', so get in touch as early as possible.
• Prepare your application. Each letter writer has different preferences, but often a letter writer will ask to see your personal statement, CV, and/or other application materials. This isn't necessarily to help you polish/prepare them, but more so that the writer can get their letter in sync with the rest of your application. This is especially important if you're applying for a position outside of the letter writer's direct area of expertise.
• Know the deadlines. Prepare a Google Doc or spreadsheet with the programs you're applying to and what the due dates are. In most cases we'll expect to see an email from each program asking us to upload a letter, but if the letter should be submitted in some other way, please indicate that too.
• Stay up to date. Writers know that plans change, and sometimes you'll need more/fewer letters than originally anticipated. Just keep everyone up to date.
• Be persistent. If deadlines are approaching and you haven't heard from your writer that the letters are in, make sure to check in with them that they know the deadlines are coming up. Gentle reminders are (usually) appreciated, but check in with the writer to see what they prefer!
• Afterwards: Let everyone know how it turned out!