I’d suggest looking at the server list on https://joinmastodon.org, select a few servers of interest, and then peruse what shows up as local to that server to find a good fit.

Also, look for indicators of active moderation and participation in the Mastodon Server Covenant if you want to avoid toxicity.

Some popular instances have been highlighted here.

Finally, dont be afraid to use a throwaway email and hide behind vpn to create a temporary account on a server or two, just to check it out.

Be kind to the server owners by deleting your temporary accounts, though.