Lord hunting is the best method not to get out numbered. King,marshals, lords with high amount of fiefs are the lords with large army caps. Aim to spank them often, or put them in prison. After they get defeated in besieging your fief, dont hesitate to sally off and hit as many running lords as you can to discourage further attacks.
Once you are fine with the starting war, you'd want to try to strike them back and recruit lords. RtR is rare to come by, so most likely you'd rely on personal relationship (release them in battles help) and starve them of fiefs. If you want a lord, hit his fiefs and he'd be likely to join you if he got none.