Nothing like etiquette but if you want your post to be readable, some best practice: Have a shortish first paragraph that would be the title of the post on the threadiverse. Mind that it will also appear as the first paragraph in the content of the post.

Your toot must not be an answer or it won’t fediverse. All answers to your fediversing toot on the twittoverse side should be consider comment on the threadiverse side. But depending on how well both instances are federating, not every answer might show up both sides.
Usually, first level answer toots fediverse well into Lemmy (and I supposed to any threadiverse software) but not all Lemmy fist level comment reach the twittoverse. Deeper answers might fediverse or not fediverse depending on too many factors for us to expect too see them.

If you want to have a rich conversations, and interact fully back to people answering you, you better have also a threadiverse account.

And a rule of thumb to ensure federation of a community to your instance, whether you’re also on the threadiverse or you’re on the twittoverse, is to subscribe to the community before posting anything.
If noone from your instance is subscribe the federation barely exist and you can’t be sure that posts are share between instances.

Here is a community dedicated to the kind of test you’re doing: [email protected]