How to succeed in IB group placement

Do it early and don't be afraid to be proactive about it.

Explain your background and (this is absolutely key) your motivations for joining the team. At least at my bank, it's the juniors who form the main momentum of opinion with the VPs / EDs weighing in (and their views can hold a lot of weight). So don't underestimate the importance of their views (MDs at least at my bank aren't involved in intern placement). I'd have some great questions for your first conversation that you can use as ammunition for your motivations in subsequent discussions - try to (if you don't know already) understand whether your preferred team has some well-known or longstanding MDs, has some interesting deal track record, etc.

If you personally have a relevant background (interned in a similar team previously, study a relevant topic, etc.) bring it up.

This might be obvious but some don't do it - ask to speak with others in the team. Your goal is that every relevant person should have spoken to you. 

Also, have a script. Unless your "interviewer" in the team guides the conversation, ask how they would like to use the discussion. If they'd prefer, you'd like to explain your background and motivations (keep this brief - let it be a conversation, not a monologue), and let them ask any questions. 

Have questions of your own. Even if you've asked them to other people, you can ask again (I'm not exactly going to read the transcript of what my colleagues discussed with you, and even if I did, you can always say "I talked about this with X and Y, but I'd like to hear your perspective). Don't ask binary questions (how many MDs are there in the team) and try to come up with questions that (A) indicate that you are genuinely trying to understand the team and not blindly asking to join the most popular one (in spite of B, I think it's more than fair to ask why your "interviewer" joined the team themselves), and (B) are unique and make your interviewer remember you (e.g. not "How is the culture in team X?" because literally everyone asks it and you'll have a canned answer)

If you're not interested in joining a team, don't speak to them. It's a waste of everyone's time, and (unlike networking for recruitment) there's no scenario where you don't join any team, so you don't need to. Plus, if an unpopular team which you aren't interested in ranks you highly, that increases the likelihood that you'll be placed there.