Your question is too broad, lacks any substantial plan on your part, and lacks your skills at accomplishing it.

Assuming you know nothing about webdesign, learn webdesign. Learn CSS. learn Python/Perl/etc.

If your site looks like garbage, it won't go far (or anywhere). That may also mean learning how to use photoshop/gimp/whatever or hiring someone to make your dream an attractive dream.

Make it accessible to people with special needs. https://www.section508.gov/ I suspect you're not a government entity, but making your site accessible will help your dream in the long run.

Set a budget for your project that will allow you to live comfortably.

How many people are sustaining this project? How will you recruit volunteers (such as the admins on Lemmy or Reddit)?

Research hosting platforms and monthly costs. How will you make money or at least fund your social media site? People love website advertising so much that Ublock Origin and Adblock have a big user base. Ads might not sustain you. Tiktok also sells stuff besides being a social media platform.

What niche is your site trying to fill? What is the purpose or advantage of using your site? Some people like X(twitter). Some like Bluesky because it's not X. Some people like Facebook because there's already people they know there. Some people avoid Facebook, because the user base is aging. For people not liking the Youtube sphere, Rumble arose, as did Peertube, Dtube, and others. Some people like discord. Some people dissatisfied with discord chose stoat. When Digg was messing up, Reddit stepped in. When Reddit started annoying its users, there was VOAT, MeWe, then the Fediverse (including Mastodon and Lemmy) arose. Snapchat arose promising people sent message that disappear so that people who didn't understand screenshots could post intimate images. Are you competing with Threads, Flipboard, Instagram, Mix, Quora, 4Chan, Stack Exchange, Steemit, Raddle, Matrix, Slashdot, Digg, Imgur, Hive, IO9, 9Gag, PixelFed, FARK, Twitch, YakPlakal, or something else?

Who is your target audience? Who are they and why would they choose your site?

So what is your plan to market your site? How will you reach that audience?

What is your five-year plan?

Have you done a premortem on your plan?