I feel like it would be courteous to tell them that you are currently experimenting with the other unit as a vacation rental and that there is a possibility that you might need their unit vacant in the future too but for the time being they are more than welcome to stay and you heard good things about them from the previous landlord (if that is true).

Obviously do this in a manner that is still “friendly” --- you can remain still courteous while kicking someone out.Also as a matter of “courtesy,” I would send the tenant a mailing package by certified mail, return receipt requested.

Just a short and courteous introduction is good. 

I will e-mail him a question and usually receive an answer (clear, concise and courteous- the golden combination!)

Be friendly, courteous, polite etc.  

Just be courteous in your dealings...Good luck to you!

Be courteous, but professional.

Wanted to be courteous and introduce myself to the community. 

I decided being on time, under promising and over delivering, simply doing what I said I was going to do, being honest, being clean, courteous and professional, were going to be the foundations I was going to build on.

You have to show up in person, smile and be courteous to the folks there, and see what they need to approve your work.