It really depends on you and how you make a connection. For me, I ask for the question they desire to have answered, a nickname or first name, a nickname or a first name of the other person if there's one involved and sometimes I need to see a pic(appropriate of course) of that person I'm doing the reading for or one of them and this other person their concerned about. I rarely ask for a picture though, a name and question is usually good enough for me.
Also, it may depend on what method you're using. The best you can do first is if you have a friend you speak to online ask them if you can do a reading on them and use different techniques and see which is best for you. The best you can do is trust your intuition.