if you're actually new here, just do what you want to do, as long as you are nice to others.
if people tell you what to do, don't take it personally: some people have not yet figured out the concept of personal space. that's okay, I guess. if they keep doing it, you can tell them to fuck off or block them or something.
you can use Pleroma's subject feature or Mastodon's badly named CW feature to attach a summary of what you're posting, this can be useful for letting people pick and choose what they want to see. it is true that Mastodon hides all messages with CWs attached to them by default, but this isn't a form of self-censorship. if that seems like something you want to do, then do it. but, don't feel pressured to use it. don't give others the power over your own experiences.
there are two things I would suggest doing, however:
1. attaching image descriptions when possible (this isn't possible in Pleroma frontend, but can be done when using Mastodon frontend on Pleroma, and Mastodon itself always supports it, and all the mobile apps you would actually be using support it), this is nice for people who are blind -- there are actually blind users of the fediverse and they have expressed appreciation for this feature.
2. marking stuff that would be inappropriate to display in public as sensitive or NSFW. in mastodon (and mastodon frontend on pleroma), you can do this by clicking the eye icon which appears when you attach an image. in pleroma frontend, you can do this by tagging the post #nsfw
beyond that, please aspire to give everyone their own personal space. this platform isn't twitter, and the fact that most generally give each other the common dignity of having their own personal space without others coming into it and telling them how to use the platform, is generally seen as a feature.