Because Lords are very powerful, there is no chance for a fast win in general, but your heros will grow stronger soon. Orc troops give higher bounty and your better map control makes it more easy to gang hostile heros. Try to dominate every crossing with strong mages like Antonidas or Morgul. Losing their outpost-protecting towers will set the orcs under pressure. They need to buy regeneration stuff for their lords and move to defend them from time to time. That makes them less capable of acting.
Always carry teleportation scrolls with you, in case towers are pushed. Losing towers means losing map control and a good reward for every orcish player. Note, that you can repair buildings with your workers. You should always do so, because a nearly dead tower can be killed easily by one not even strong hero.
Always check the map for catapults. Those guys are your death. Although they are easy to destroy, they crack your towers within seconds.
Before moving out, trying to kill a lord, hire Dragonhawks. Those units are very tough and deal heavy damage to lords. Focus Rokan or Cairne before you try to fight other lords. Those guys are standing alone and are more easy to kill than other lords, that have a brother in arms right next to them.
And finally watch the score board regulary. Orc players will start to upgrade their troops soon to dominate the path to your castle. If they do so, you should really measure up.