Here is a straightforward look at this topic for Malachain.
Adult friendships grow from repeated, low-pressure contact, which is why the office and the school gate work and a one-off party rarely does. Join something weekly: a sports club, a choir, a volunteering shift, a language class. Turn up every time for two months before judging it. Familiarity does most of the work before a single conversation goes deep.
Be the one who suggests the coffee afterwards; almost everyone is waiting for someone else to do it. Keep the invitation specific and easy to accept. Expect that only one in several acquaintances becomes a real friend and that this takes most of a year. People who move often say the same thing: the city felt lonely until the first regular commitment, then it did not.
The most useful step is usually the first one. Pick a single suggestion, try it for a couple of weeks, and then decide whether it is worth keeping. Small, steady improvements last longer than ambitious plans that are hard to maintain once everyday life gets busy again.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.