Setting a fair increase
Compare your rent with current listings for similar units, factor in tenant turnover cost (vacancy plus make-ready often equals one to two months of rent), and check local rules: several states and cities (e.g. California, Oregon, parts of New York, Washington D.C.) cap annual increases or require longer notice. A modest increase for a good tenant is often more profitable than a vacancy.
Turnover math
If a $100/month increase causes a tenant to leave and you lose one month of $1,650 rent plus $800 make-ready, you need about two years of the higher rent just to break even.