My biggest tip is to remain consistent with your requirements... this will prevent early turnover of apartments... stay 100% on customer service and get your residents involved in some of the ideas for the property... the more imput they have the more it feels like home.. hope that helps!
Due to the comments I've heard from prospects, I strongly believe my 100% occupancy is at least partly due to my reviews on apartmentratings.com. Every time you renew a lease or someone thanks you for something, hand them a brightly colored card and ask them to post a review.
For retention, make sure to have something to offer them. We offer lease renewal carpet cleans, but even though that may be a "carrot" to the resident, our reason is to extend the life of the carpet. We have a clubhouse space so we also have parties throughout the year. Pizza or ice cream are big hits. Ask your vendors to provide some door prizes to give out at the parties. If you don't have space for parties, small seasonal gift bags are nice. I spent less than $1 each for gift bags last year and they were much appreciated because it's the thought that counts!
Not raising rents and offering any rent concessions to re-lease might work to keep most of their attention off even looking/considering for alternatives....particularly if you are in a market where lots of properties are offering move-in specials in the form of free rent all around them.
Tough to say without knowing your market though I guess.
I am not in the business end of knowing any cost analysis of turnover costs vs. offering concessions on renewals but my common sense tells me during a down economy, and competitive market this would be at the top of my list.
Many things get renters into your apartments and many things potentially make them leave, but the one constant in any equation on the issue comes down to $$$ which is usually a prime motivator.