If you are interested in a military career my own duchy (sig has link in on a phone atm) has a very strong focus on the military, plans to have a military academy to help train players and is always recruiting.
Personally I’d suggest making yourself known in each of the kingdom discords and talking to people and getting to know the communities. Each group has its own biases and quirks but for the most part Selene is a pretty chill server with only occasional drama.
Depending what sort of pledge you’re looking at if then work down the ‘ranks’ as it were and focus on the locality where you wish to play.
Of course there’s always the option of holding out till domain selection so that you make sure you get the best group/location/tribe for what you want to do.