I suggest adding some relays otherwise the only posts reaching your server will be things you yourself have followed, which makes hashtags a bit useless.

My current active relay list is: https://bigrelay.social/inbox https://relay.toot.io/inbox https://relay.intahnet.co.uk/inbox

But those are just what works for me.. not any particular recommendation.

Then follow lots of interesting people. Look on other servers if you're stuck, eg. the live feeds on mastodon.social. The more you follow the more conversations you'll see and find more interesting people. People who boost a lot are a goldmine for discovery (some people make a hobby of boosting eg. https://mastodon.social/@lisamelton).