I have done this several times. You situate yourself in places where you will meet a bunch of other people and aggressively socialize (as in pushing yourself to go out and mingle with strangers even though it's a lot of work, not force your way into conversations).

You'll have to introduce yourself over and over and of course the basic questions are where you were, why you left, and why you came to where you are. You have to do this often enough that it sort of becomes like a pitch that you need to refine to avoid boring others or exhausting yourself, so it's a good time to decide how you want to appear and basically redesign your life to the extent that you feel like doing that.

A downside from the economic point of view is your lack of an existing network, but then again you'll also be open to opportunities you might not have considered otherwise, and you'll also be the New Interesting Person for everyone you meet. If you can tell interesting stories about where you've been or what you've noticed in where you just arrived (without making them all about you), and are in turn good at asking questions and actively listening, then doors will open up for you.

Pay attention to appearances and think about yours (what you want it to be and how much work that will take to maintain) as it will have a big impact on your encounters and subsequent experience.

Signaling that you are valuable fot that network. Practical example would be having repositories on github that signal skills and genuine interest in a topic.

Companies (which are netowrks too) would reach to you eventually, or as other are saying meetups, etc. But I think the key is signaling value.

Meetups, volunteering, hobbies (climbing gyms, etc). Essentially use a similar interest/cause to break the ice with others.

Dance lessons and meetups are a great way to meet people in a social atmosphere. Board games might be good if you're into that. Join an adult co-ed sports league, and if you're not particularly athletic then do kickball, Cornhole, or ping pong. Join a hiking and outdoors club. If you work remote, work from a co-working space. Attend meetups. Explore local live music scene.

Get out and meet people?

For starters, wouldn't said person work at that new place? They can meet colleagues there and become friends with them. Or clients, or people working for clients, or suppliers, ...

Wouldn't they also go out at bars, restaurants, cafes, etc?

Join a church, or other Meetup group. Join a union, or other vocational association.