Use hashtags that are fairly active. You can search for them before posting to get an idea which ones to use. Even if your toot doesn’t have a good active hashtag, post it. People will check your profile before following and are more likely to follow accounts that are interesting and active.
Also consider posting just for yourself. Thoughts you want to note for later, things you found interesting and want to go back to. You likely aren’t going to get a huge amount of followers on the fedi unless you are well known unless you start following A LOT of people and you give them a reason to follow you back