- Contact the Worton's mother, Desette.
- Lysander, Proetho, and the best two other heroes (max level 30)
You'll have to do a lot of fighting on this map, as the four computer opponents (Red, Teal, Blue and Orange) have two towns apiece. You don't have to take all the towns, but you might as well for the extra experience and the added troops.
So group together your units into two armies. You'll receive three more high level heroes before the end of the campaign, so I'd recommend putting the two random heroes together into one army (since you don't really need to develop them any further) and putting Lysander, Proetho, and the five starting troops together into a second army. Then let Lysander's army do all the work while the other army picks up stuff.
To start out, there's only one way to go, so kill all the creatures you find and loot all the resources and objects on the ground, and push forward. Along the way you'll find a prison with a level 25 hero inside (I believe it's always a General). You can either add the hero to Lysander's army (in place of, say, the pikemen) or you can add him to the army with the other two random heroes. Since you need to make Lysander as powerful as possible, I'd suggest the latter course.
Eventually you'll come to a Red town. It shouldn't pose much of a problem, and neither should the second Red town to the northwest. When they're both yours, Red will be eliminated, and you'll have a nice base of operations. Plus, the second town is protected by the first, so you don't have to defend it against attacks. But eventually you might want to think about upgrading the first town to have a castle.
Now you have a choice about where to go. You can either go south (towards Blue) or east (towards Orange). They're both relatively easy to conquer, but attacking Orange first makes your lands easier to defend, so that's probably the better choice. Meanwhile, keep building up your towns, and alternate between having champions and angels. (You probably won't be able to afford all angels.) Then, when you're ready to move on to your next conquest, upgrade your army to have Lysander, Proetho, champions, crossbowmen, monks, champions, and angels.
Once you've taken Orange's and Blue's towns, you again have a choice. You can either attack Teal (to the southwest) or you can finish off the mission. There are a few skill and attribute buildings in Teal's territory, plus the experience for killing Teal's troops, so that's the better choice if you want to build up your heroes.
Otherwise, head southeast, but don't attack the garrison. Instead, take the bridge south of the one leading to the garrison. It'll be guarded by high level Might creatures, and they'll put up a good fight, but it'll be your last battle of the scenario, so it doesn't matter if your troops get beat up or not. Then just visit the tree of knowledge and take the dragon portal to Desette to finish the scenario.