Let people talk
While experienced groups often have a rule that says "keep out-of-characters banter to a minimum", that can go out the window for a fresh group of strangers. Give people chances to chat. That means keeping a big gap between "everyone is here" and "let's start the game", so people can get to know each other. It also means pausing the game for a few minutes if another player has an amusing OOC-tale to tell (so long as it isn't boring other people)
You might even realise you lost almost the entire evening to random banter, recalling other games and brainstorming ideas. That's fine, it means that next time you'll know each other better.
(The last time I set up a new group, it wasn't until the 3rd session that we really got into the game proper, but we did get to know each other quite well)
Consider food before the game
One of the great things that I try to work into every group I can is to include at least one meal in the game and preferably have it before we start playing. If at all possible, get a group member to prepare it or everyone bring something. This gives you a great time to catch up or get to know each other, gives you a bunch of easy topics (self prepped food is good talking material) and helps give you a nice atmosphere. It also gives a natural transition into the game when you call "let's clean up and get started".
Design characters together
For a number of systems it is actually a rule that characters are designed together, at the table. For others it is not. Regardless of what you play, it is important that in the narrative these characters are connected.
This allows you to skip over the awkward "five guys who don't know each other suddenly leave everything behind and go on a mighty quest" phase of the story, which will only be worse if you do not know the other players.
Instead you can jump right into the interesting parts of the story, and everyone has good reason to act friendly to the other players.
I would make it a rule that each character has a positive kind of relationship with at least half the others at the table. (Friends, colleagues, family, warbuddies, whatever, as long as they are in good standing together).
Lead by example
The GM often sets the stage and is a sort of measure of what is good conduct at a table. So make sure to give the right example. This is more of a general advice thing as even with people you know the GM often sets the level of immersion.
But especially with new people it is important to show them that it's perfectly fine to act like a fool with these people you do not know. Talk funny voices, make silly jokes, but also don't be afraid to pour on good descriptions and be serious when required. Others will follow your lead, so make it a good one.
Tools for getting to know others
In addition to this amazing kind of group-building activity called "roleplaying" (You probably heard of it? :P) there are also many other games that you can play that don't take up as much time and let you get to know each other.
Unsurprisingly, pick the ones that somehow factor storytelling into them. My absolute favorite for this is Dixit, as it is easy to explain and lets you see how people think. Other runners up are Cards against Humanity (requires an adult audience of people not easily offended. If you doubt whether or not this game would go over well, do NOT use it. It's as easy to get to know people as it is to sour the mood.) and Once Upon A Time
Games really do bond people together, especially the ones that force them to talk.
Also that other tool
Definately consider running people through the Same Page Tool to make sure everyone understands the kind of game being played. This goes for all groups, but especially when you don't know what to expect, this is a good one. Nothing ruins the mood like different expectations.
Keep in mind that the Same Page Tool is not a survey, it is a declaration! Use the tool as it is intended, or it will not help.