This is not complete by any means but this is what I did (recently):

• Explore around: Currently there's an influx of new user and communities (subreddits) being created. Total users has doubled (give it take) in 10 days. Active monthly users has increased 6x in the same 10 days
• Try to engage: For many (most?) of us this is a brand new place. Not so long ago it felt rather quiet (I remember taking a look a few months back and thinking "It's a cool idea but there's not enough content") As a forever lurker, this has been easier said than done. The vibe I get (YMMV) is from early Slashdot / Slashdot clones, only much more vibrant. I haven't seen something similar in a really long time
• Missing content? Either you wait (keep exploring) or become proactive. Even if you intend to hand it over down the line, create/start building any community you are missing. For those that are joining after you, it's reassuring having a moment of "Hey, here there's also interest in $RANDOM_THING"
• Be aware of size: Recently I was taking about this. Some "not so large subreddits " have 10x users subscribed as users in the whole "lemmyverse"? "lemmy ecosystem"? (I'm still not sure how it's named)
• The system is quite new and has had a sudden explosion in popularity. Be prepared to see some rough edges here and there.

A couple of things that might be odd to get your head around:

• Instances: Although you can think of instances as a "whole reddit" they all work together. Both of us are on different instances and I'm commenting on your post. I'm not even sure without scrolling on which server resides the post
• Fediverse: The collaboration is not constrained to instances alone. I was engaging (from Lemmy) with a post originating on a different platform (kbin) and checking how it looks on a third platform (Mastodon). The analogy might be bad, but think of commenting from Reddit on a post originated on digg and checking how you see/comment on it from Twitter.

But the most important part, enjoy your time here