-make peace and take advantage of it by building your resources (ie troops and money)
-promote some companions and give them as many troops as possible
-don't be in a rush to go to war. your empire has only just begun. solidify its foundations. put some troops in your garrisons, maybe 300-500. don't have to be elite.
-when war time comes, go for towns. that's where the money is.
-don't war with everyone around you. see if you can ally with all your neighbors aside from the one you're going to attack beforehand.
-now's the time to start grooming companions for either a promotion (prisoners, healing, troop numbers....) or tailor them for a specialized role in your party (inventory, healing, engineering, tactician, prisoners etc)
-don't go promoting people willy nilly. keep in mind that you'll need some people to hang around.
PS don't use the cheatcode to infinity rank any companions. that'll drive their price waaaaaaay up.