the best race to choose for quick gaming is the undead. They have a massive halberd bonus with only their archery to lose, which for this strategy is unimportant.
At the beginning of the game, buy the halberd units. On the map, avoid the Orcs of the South and the Men of the West for a bit; they're hard because of their axe throwers and javelins. Of course, if you enter a battle with the OotS or the MotW and they DON'T have axe throwers or javelins, then by all means, fight them; they won't be as hard.
In normal battle, just hold down the space bar with the halberd units selected, which sends a line of halberdiers down the same lane. Naturally, the CPU will follow up by sending units down the same path. Your halberdiers will crush them. Don't worry about other units in other lanes; the gains will catch up with the losses. Keep an eye out for charges. When you can charge, charge with the halberdiers.
hope this helps :D
24 is easy it just takes a while to get it right... aim three bombs where the king and queen are. the knights fall - knocking down the floor - the king falls and pretty easily the queen falls - the last one... either it topples and kills her or your going to have to get her in blast radius :D