What is in your lease about when rent is due when it will be considered late, what the penalties will be and when you will take more drastic action? The first rule of good tenant relations and rents is to have a clear set of rules and instructions for your tenants, and then you must consistently enforce your rules.
Not to harp on good communications and written instructions, but it's how to avoid problems in this area as well. Your tenants should know when and how to report a maintenance problem. The easier you make the process the better. They need some idea of how soon you will respond, both during a regular workday, as well as at night or on weekends. Knowing will reduce complaints. If you're calling in repair vendors, make it important to them to be responsive to your tenants and to keep you informed if there are problems in doing so.
Don't favor some tenants over others or enforce only the rules that upset you the most. Every time you fail to follow through on written lease rules, you weaken your ability to do so in the future. It could come back to haunt you if things go all legal on you.
From door flyers to email, it's not a problem to communicate with your tenants, no matter what their schedules. Social sites are changing a lot of things, and this is one of them. Communicating with your tenants via Facebook, Twitter, Google+ and other social sites will strengthen your relationships. You may even use a Twitter account to communicate directly with them about repairs and other concerns.