You should have paperwork ready to make sure you can submit an application as quickly as possible on a place you like. The summer rental market is always competitve, so if you have the paperwork, you'll be ready to apply quickly. You do not need to give this paperwork to anyone until you are ready to apply.
Here's about what you'll need for yourself and a guarantor:
1) the guarantor needs to make 80 to 100 times the monthly rent.
2) first two pages of 2011 tax returns
3) 2- 3 recent paystubs
4) checking and savings statements
5) letter of employment stating how long you (or your guarantor) has worked at the company, position, and salary.
6) for you, you'll need a letter from your landlord stating how much rent you paid, how long you were there, and that you were a great tenant.
Also, if the guarantor is self-employeed, the requirements are a bit different.
Some landlords require more information, some less. However, if you have this information ready to go when you're looking for an apartment, you're more likely to get the apartment you want!
If you have any questions, don't hesitate to ask, and good luck!