As you consider asking professors for letters of recommendation, please remember to bring each letter writer a FERPA waiver form. The forms are available at the Registrar's website. Here's a link to the most-used form...you need to turn in one copy to the Registrar's office and give one copy to each letter writer. This St. Olaf waiver is different from a waiver you may have signed for the receiving institution. The reason to sign a waiver is so that the receiving institution can be sure that the submitted letter is an honest and frank appraisal of your abilities.
Faculty are asked to write a large number of these letters, so make sure to ask far in advance of due dates. It's a good idea to supply letter writers with lots of information: a resume', a statement about your motivations for the position you are seeking, a degree audit if the faculty member is not your advisor, an organized list of due dates, addresses, websites, etc.
Finally, if you are still a young college student...make an effort to get to know your professors! Visit during office hours, either to ask questions about class or just to introduce yourself. Eventually you may want letters of recommendation from these people!