I disagree with this advice. Although you do submit your letter writer's names through AMCAS, you should DEFINITELY be asking them to write you a letter yourself. They should not be surprised when they receive an email from AMCAS. If you had a professors during your freshman year that you would like a letter from, my suggestion is ask them to write it as soon as you can, i.e. right after the course ends, so that you are still fresh in their mind. Then, when application season rolls around, you could ask them if you could use that letter, but just have them change the date on it. They could also add in any updates, for example if you've done more work with them in the interim.
I suggest getting a subscription to Interfolio if you will be asking a lot of professors for letters long before you will be applying. This will allow professors to upload letters securely for you, and you can have them all in one place.