How do you indicate to a school that they are your first choose besides early decision?
If you are writing an essay that would just be going to that one first-choice school, you could perhaps include that information in your essay somehow. You could also ask your Guidance Counselor to include your preference in the recommendation letter he/she writes for you. Care should, of course, be taken to ensure that that comment is only included on the letter going to your first-choice school! If you're indicating a first choice, it would be beneficial to indicate a reason/reasons why you feel that way. Some reasons would obviously not be very convincing - "All my friends are going there", "I've always wanted to go to an Ivy League school", "My boyfriend/girlfriend is going there", etc. Your reasons should have to do with what you know about what the school offers and how you would fit into that environment.