Take your time, there's no need to rush to look for an alliance. For a new player in the game, Global Chat could be treated like an open alliance, with lots of helpful advice and some resource help too, as well as beginning to make friends within the game's community
Some players will have different opinions on when it's best to start looking.... on leaving player protection, settling 2nd town, when thinking about moving your early towns
Then when you feel the time is right, having learned a little of the game from new player guides in the Forum, and in global chat, a new player should think about what they want from an alliance.... help with resources, advice, help with growth.... advice on technical parts of the game like diplo and military... where a larger alliance, or a training alliance might be best....
Any alliance will try and help their new players with resources and advice, with training alliances, that might be more focused, but remember, a training alliance is almost certainly only for temprary membership, where you will likely be moved on when reaching a certain stage in the game... (number of towns, or population, length of time)
There might be players who would like more of a challenge, joining a smaller alliance that is less likely tto be able to help with resources and if the other members are also reasonably new to the game, they might be only slightly more advanced than a new player and unable to help with advice, in that case, an alliance like that can grow together, learning the game together, getting advice from global chat when needed, forming something of a strong bond
Some alliances might be more military-minded, some less, some not at all, some might be based in 1 region of the map, some spread around the map....
When looking for an alliance, there are many alliances that a player would think of as ok, but only 1 or 2 that would feel like "the right fit", an alliance they would feel most confortable in and enjoy being a part of
Check the alliance profiles of people in Global Chat, alliance profiles in the alliance list, asking about alliances in Global Chat can also be a good source.
If an alliance interests you, contact 2 or 3 members asking them what being a member is like and what is involved, could also ask in GC if that alliance is known and has a good reputation, then if still interested, contact the allance leadership with any further questions, what's expected from members, what the alliance believes in, if they play along a certain path such as trading or military, how the alliance might benefit from that player being a member and how the player can benefit from being a part of it,.
Best to find out as much as possible about an alliance, before joining to avoid choosing one that isn't right, and to improve the chance of find one that is
For those in the game that choose to be in an alliance, I believe the vast majority like to think of their alliance as their family within the game, alliance mates that are friends as well as colleagues
the main thing for any player, it's you that should choose your alliance, not them choosing you, good luck in finding the one that's right for you
I'm happy to be corrected on any of these tips, or if anyone wants to add any amendments to improve on the advice.... it's there to help, so improving the help it offers can only be good