1. Read the reddit post (to know the server staff's expectations and to give you an idea of what to expect from the server): Reddit post here
2. Join the discord
3. Follow the discord server guide
4. Get whitelisted and join!
(Bonus): Watch the video below
What next? (alternative to the video)
On the discord server, you write your name into the #whitelist-names channel and wait to get whitelisted, which can take up to an hour.
When you get whitelisted, be sure to read the entire message, as it tells you what to do next. Alternatively, you can just read the in-game welcoming message that tells you what to do.
After completing those tasks, the only thing that remains is actually playing.
For ideas, check out the wiki!
Preferably Gameplay options and Structures + progression path
Note: Ignoring the welcoming message and its tasks is violating rules: 11. 14. 20. and the lack of information that you get from it will be noticeable later on in your gameplay, therefore it's highly advised not to ignore it.