I like to send monthly statements via email to tenants, which also has our web portal to make online payments. I give the tenants an opportunity to let me know if rent is going to be late, if there is a valid reason, we will agree on a date to make the payment. If rent is not paid on the agreed date, I charge our late fee and any additional fees associated.
I also do not charge tenants a late fee, for a first offense, we all have made mistakes, are forgetful and things happen, it is out of courtesy.
My prior and current business is/was driven by poor landlords, when tenants understand you appreciate them and care for them, it does wonders! Never jump to conclusions, never take offense and always give them opportunities to redeem a mistake, within reason of coarse. Some may take the standpoint that tenants would take advantage of this, hire a quality management company and you don't have to worry about this, personally I would rather loose two months of rent waiting for the right tenant. In fact I have on a few of my properties and I could not be happier, I spent $25,000, upgrading two apartments, tenants pay on time and the units are spotless.
Personally it is important to remember, in giving we should never expect anything in return.
I would have to disagree with the last post, if she is in fact a good tenant, some leniency at times is worth it. Of coarse we are all here to learn how to make money but we can't always be focused on $$ signs.