I’m gonna give some different advice to the rest of the comments:

I think the most important thing is to consider what you want to achieve out of joining a party. On the face of it this sounds like opportunism but hear me out before you jump to conclusions prematurely.

Do you want to develop your skills with activism in its many forms?
(Creating agitprop, making speeches, recording, making effective social media posts, and of course the pointy end of activism like hardcore protest strategy)

Join your local affiliation groups that are doing stuff like climate activism, Stop Cop City, anti-war protests, Palestine solidarity groups etc.

Do you want to develop your understanding of theory?

Join a local reading group or a larger national one like the PSMLS (did they have a split or something? I don’t keep up with the drama…)

Do you want to do mutual aid work?

Generally your local orgs are the best (and often the only) option.

Do you want to learn how to canvas and do the more formal party organising work?

Here I’d tentatively recommend volunteering for a campaign like Bernie/Jill Stein/Cornel West/the current PSL candidate. This will likely require you to hold your nose at least to a certain degree but if you want to learn the ins and outs, getting irl experience by rolling up your sleeves and doing the work is the absolute best way to do it.

Do you want to build connections and networks?

There are a lot of good options here but I’d recommend aiming for the stuff that is closest to the labour struggle/similar types of unionism (e.g. tenant unionism, radical prison outreach orgs, etc.) or to join a national organisation (assuming it has an active branch in your local area) such as the DSA(!) or even the CPUSA(!)

Remember that if it’s about building a network, you want to leverage the reach of the organisation you choose to affiliate yourself with so the bigger the org on a national as well as a local level, the better.

Do you want to form a vanguard?

This one is a little bit tougher. I’d recommend a good local reading group as the starting point but the other option would be to play the angles and drive a split in a larger organisation that is terminally revisionist like the CPUSA or the DSA (sorry CPUSA and DSA members, I know that your local people are probably really solid comrades but the top end of your orgs are absolutely dismal - I know you know it too and I don’t intend to shit on your local branch).

The ethics of causing a split are a very big discussion that is kinda tangential to the purpose of this comment. In cases like the CPUSA and DSA, I’d argue that they are already very much in motion (especially in the case of the DSA) so this is significantly different to joining a unified party and acting like some Trot wrecker within those ranks; a split where it’s only you splitting is the same as getting booted from a party. A faction of malcontents is a necessary precondition for a split and while you shouldn’t go fomenting disunity within a party, if one already exists then so be it.

There are probably some other aspects of development that I haven’t given attention to here but this is just a quick rundown off the top of my head for you to consider and to use as a point to spring off from.

Note that these things don’t have to be mutually exclusive; your local mutual aid group might also be deeply involved in activism and it’s likely to be a decent place for developing connections in too. You get the idea.

Party-hopping is poor form, generally speaking, so do commit to a course for a good while unless you have genuine cause to leave (corruption, gross mismanagement of the org, the org goes dormant or is disbanded, serious misconduct from org members, irreconcilable ideological differences etc.) although you can also pick and mix, depending on what your involvement allows so you might be able to be part of a national org while dedicating some time on the side to local unionism or solidarity/mutual aid work etc.

I guess in a sense what I’m trying to impress upon you here is that it’s okay to treat organising work in a similar way that you would a career. Obviously it shouldn’t be about ruthlessly selfish personal advancement at any cost but considering your own personal strengths, your passion, what areas you want to develop, and where you want to take your organising work is actually really commendable imo, especially if you plan to be a leader of some sort or you want to become part of a backbone of an organisation because you have critical skills and experience in certain domains; anyone can join and org and just follow along but almost invariably there will a desperate need for more niche skills like public speaking, skilled artists or organisers, and stuff like administration. So think about what you want to get out of joining a party/org and consider what you want to get out of a mutually-beneficial arrangement with them as well as where you would like to end up focusing your organising efforts on.