With someone I'm not sure about I usually start with the Legallizaton issue, that conversation will usually tell me what I need to know about there feelings on the subject without putting yourself at risk, If they are pro legalization and appear to be of like mind I then smoke someone else's weed with them 1st (I don't want them to know Im a dailly smoker and have a few OZ's in my room yet) If it is someone else's, then your inviting them as part of the group without saying much about your habit and you already know they arent going to freak due to the legalization conversation.