As well as filling in your profile, it's a really good idea to also pin an introduction post about yourself to your profile.
Pinned posts let you write a lot more than profile texts, and let you attach photos, audio or video. You can even reply to your own pinned post to create a pinned thread.
More info including how to pin posts:
https://fedi.tips/how-do-i-pin-my-posts-on-my-mastodon-profile
For technical reasons, pinned posts and pinned threads are distributed much more widely than ordinary posts.
@FediTips Pinned posts are a great way to share detailed intros and media at the top of your profile, making them easy for visitors to find. However, as far as I know, pinned posts don’t get extra distribution in timelines or the wider fediverse—they’re just more visible on your profile. Still, they’re a fantastic tool for helping people get to know you!
Pinned posts are treated differently at a technical level by Mastodon, they are (currently) the only type of post that is automatically "backfilled" to any server that views the profile. This means everyone who views a profile will always see all of its pinned posts.
Normal posts don't get backfilled, so they may not be visible to everyone, which is why some profiles might look blank:
https://fedi.tips/why-does-someones-account-page-look-completely-blank-is-it-really-blank
Profiles with pinned posts never look blank because of backfilling