One of the biggest things that you can do to cultivate a good relationship is uphold your end of the lease. If it is written that you are to take care of the repairs in a timely manner, then do so. If you are supposed to come around in person every month to collect the rent, stick to that. Always do what is expected of you as per your original agreement and that is a wonderful place to start.
Another thing that is extremely important in having a good relationship with your tenant is to go the extra mile. Now this doesn't mean you need to come around to their apartment and cook them dinner every Friday or shower them with gifts. A message every now and then simply checking in, however, can do a great deal to help your relationship. Ask if everything is okay at the rental property. Check if there may be anything you can do or help with in regard to the housing. If they respond that there is, then go and help them. One thing that I know some of the landlord's I have had did that hurt our professional relationship was offering help and then telling me that I should do it myself.
Speaking of the professional relationship, this is one of the biggest things. You should always keep the relationship between yourself and your tenant professional. You could be renting to your best friend, but business is business and many people seem to forget this. It is much easier to let one's friends get away with things than people you don't have a personal connection to. When it comes to property management, there really should be a separation. The relationship between you and your client is extremely important, so you want to do everything you can to strengthen it.