How fast do you want the return on investment on the new market? I.e. do you want to achieve results in a rather short time or I you willing to wait for a long-term result? 

What kind of markets will your products fit in to? E.g. look at the markets with the same technology level you are in today where your products will fit. 

The geographical distances are not so important. They are easy to overcome. The mental "distance" is more important. Select a country where the technology of product level is about the same and they way of doing business is similar to your home market. 

Make sure the market is expanding.