You mean, just pick a side at random, and barge in? The latter would certainly be rude, but the former I'm sure I'm getting wrong.
My question, answers, and understanding is based on my experience in street evangelism. In a team, or by myself, would go on a street, in a park, or on campus and hand out tracts and if possible, engage in a conversation with people in order to share the Gospel with them
With Jehovah's Witnesses, or any other cult, I would go to them and if they're in a conversation I would observe and wait my turn. When appropriate, I would seek permission, and give my input.