I would say in general no matter which Lemmy instance, be conscious of using others' server and hosting space.
For example, don't "comment to save for later". Don't upload unnecessarily large photos/media, but you can obviously link to images/video from your own server or elsewhere on the 'net.
Try to engage more with discussions where they are genuine, try to stay away from Redditisms that don't add anything like saying "this", singing lyrics in comment chains, shitposts and copypasta in non-meme communities or where it's not called for.
The rest are dependent on the rules and philosophies of the Lemmy servers and communities you visit. Read them and follow them as best you can.