For polishing the brass I use Flitz polish, as recommended by Alembic. Then, once it is shiny, I use my fingers to rub on a little Alberto VO5. Then gently wipe off any excess with a clean cloth. It’s an old fashioned hair conditioner my mom used to use and an old trick for keeping brass shiny longer. Works great on the brass on my Alembic custom Further and my other guitars with brass fittings.
But, as Jon suggests above, there is nothing wrong with letting it develop a natural patina. I have a couple of 1970s Alembic guitars on which I leave the brass tarnished. And I’ve been building an Alligator replica on which I soaked the brass parts in vinegar and salt to get them tarnished.