Tactic 1: Reign of Terror
Having so many Terror-causing units in the army means that you should be able to scatter those enemies with low Leadership values. Storm forwards as a mass and aim to get as many enemy units within 6" at the end of your Movement phase as possible. Models with a Leadership of 7 have a 42% chance of failing any given Leadership test, while those with Leadership 8 have a 28% chance. The more enemy units you force to take Terror tests, the more will flee and fleeing units are no threat at all!
Something that I've tried with mixed success is using the Skink Skirmishers to 'herd' broken units off the board. This means that they've got to advance with the rest of the army (a dangerous proposition at the best of times), and when enemy units fail their Leadership tests and flee, the Skinks chase after them. When you're already broken, if you're charged you must flee immediately which tends to make things flee off the edge of the board. The only flaw with this plan is that people keep killing my Skinks. It probably wouldn't be too hard to reshuffle the army a little and get some Terradon Riders in though, who can move faster and flee from combat with fewer worries.
just use youre stega's to terror it and let the skinks go after them.
Tactic 2: Engine of the Gods.
Keep this bad-boy at the centre of your force, being sure to employ the Portents of Warding in the early stages of the game. This wonderful power (which cannot be dispelled, huzzah) gives friendly units a 5+ ward save against attacks that originate from further than 12" of the Engine of the Gods. That means, with the Stegadon lurking slightly behind the main advance, your stampeding horde of monsters will be protected, at least a little, from the slings and arrows (and cannonballs & magic missiles) of your enemy. Great stuff.
Once you're in close, deploy the Burning Alignment. This superb magical power causes D6 Strength 4 hits on every enemy unit within 2D6" and, once again, it cannot be dispelled. So get in nice and close and cause havoc.
just use stega's special rules with one engine of the gods!