I mean firstly - as everyone has said, the things, the connections, and the experience you need are found in the established communities, so yeah, find, join, and dedicate yourself to one - you want to grow your knowledge of the game, integrate with the community, and gain experience in government.
Then, at some point considerably further than 'a few months' down the line, you may want to consider starting your own thing (and if you're actually in a position to consider it, you'd likely already know everything you need) - you'd want to get some of your friends in your tier (hopefully at least the 20's), and start planning things out. You'll need the founding group, certainly, and those founders will have to be able to get the ball rolling both economics and administration-wise - your group will be doing the heavy lifting for a considerable amount of time before your new members are able to do their part. At this point, you'd want to capitalize on the connections you have, preferably across multiple alliances to start building some semblance of a community - on top of securing a strong protectorate, hopefully one which is willing to help you wherever you may be lacking. With regards to economics and management starting off, it would be reasonable to prioritize selection, training, and raiding assistance for your new members - taking from the output of the founding group (and stunting your own growth where necessary) to present an effective and 'competitive' system of opportunities for growth. Definitely more that I haven't mentioned, since I've only looked at the process theoretically - do correct me if something is wrong or inaccurate.
But as a TLDR:
> find, join, and dedicate yourself to one - you want to grow your knowledge of the game, integrate with the community, and gain experience in government.
> if you're actually in a position to consider [starting an alliance], you'd likely already know everything you need