The main place where you'll need to do this is conveniently marked on the map with five little glowing white circles, so it's not really that difficult a decision to make.

Boom, you should soon have some paths through the trees. You can use your Meat Wagons to bomb the trees down though, just hover your mouse over a tree with the Wagons selected and hit 'A' for attacking neutral targets. The one thing to remember here is that in many cases, trees will block your way. Augment your core force with more Ghouls and head off, either directly east or start going south. Upgrade your Ziggurats to Spirit Towers if you feel like it - but if things are going well, the Elves will never even get within half a mile of your base. Then start building a Crypt, Graveyard, and as you acquire enough resources, add a Slaughterhouse (where you can build more Meat Wagons) and a Temple of the Damned (where you can train more Necromancers). Delegate the Ghouls to gather wood and take the rest of your units as a guard force on the southern edge of your new base area. Build your base more or less the same way you did in the last game - first Haunt the gold mine and then start summoning in your Necropolis. Wipe it out, wipe out all the elves too, and then start setting up your own base. When the game begins, you'll have a small strike force and will descend on a pretty much helpless Elven base.

Warcraft 3 key of the three moons