We've been pretty lucky with our tenants, we had a young couple (grad students) there for 6 years and they were great, we still keep in touch, then a quiet young woman who was never at home, she only lasted a year and then the current tenant has been with us 4 or 5 years (I've lost track).
Our strategy was to really make the place nice, good appliances, garage, etc. and then to charge near the upper end of the market range. Once we have somebody we like, we never increase the rent. So far, so good.