The best way I've found to onboard someone is to assign them a person (or two) that are their "tour guides/main contacts." Get someone to do this who is charismatic/friendly, but also shares personality traits and other attributes (match people who have researched similar topics, etc.).
This has a few advantages:
- It is a "friend" for the new person. Even if they may not realize it at the time, having someone the new person knows in a room of many faces to sit by gives them some sense of familiarity.
- Making people in charge of onboarding a new member makes sure that specific policies, major aspects of your community's culture, and other "need-to-know" things are conveyed to the new member. Especially with analytical thinkers (which I assume is the majority of people in a CS-type research group), it's quicker to onboard someone when they are initially given the information they need to succeed in the group.
- When the new member does have a question, they don't have to be afraid of appearing "dumb" by asking a relatively simple question as they can ask their "guide" privately without drawing attention to themselves (see the first point).
- If the entire group can't meet in person often, you can have a geographically-close "guide" meet the new member at a coffee shop can help make the new member feel welcomed into the group.
Spending a few hours in person with someone is the best way to get to know them and immerse them fully in your group's culture. Even if you need to get work done, block out some time before/after for everyone to socialize and get to know the new member. You could meet anywhere from a public park to a coffee shop or bar.
Video calling or a conference call is also decent for getting to know someone, as long as the call doesn't have too many people (you get to know someone by talking to them in small groups or one-on-one, NOT with thirty people taking turns speaking). Using written communication to get to know someone is next to impossible (even texting).