I reward good tenants with stable rents, unit upgrades, and honeybaked hams for the holidays (not joking).
Depending on the unit: By the time you factor in advertising, showings, taking apps, and prorated rents; basic turnover (normal wear and tear) runs equivalent to about one month's rent and goes up from there, in my experience. That's 8% of total annual revenue! In most markets that is equivalent to about 4-6 years of rent increases saved in a single year by keeping a good tenant in place and avoiding turn costs.
I have even gone so far as offering decreasing rents for multi-year leases. That's better than discounting at the beginning IMO because multi-year residential leases can be hard to enforce (in my state) and because people's plans often change. So your rent may start out at just slightly above market (i.e. $1,000) then drop in year two ($975) and again in year three ($950) at which point I offer to hold it for three more years. Tenants feel like they're getting a great deal and have incentive to stick around and not violate the lease terms. If the tenant's plans change and they decide they'd like to leave after year two or three...no problem. I let them out of their below market $950 lease and repeat the process with a new tenant starting at whatever market rent as at that time.