Moving your General to a safe distance may seem cowardly, but it actually gives you offensive opportunities by opening up spots to place defensive units.
Hazards
Environmental hazards like mud can be used to slow enemy troops as they have to trudge past your attackers.
Time and patience
If you really have a lot of time and patience on your hands, there are online leaderboards to climb in straightforward multiplayer skirmishes.
Unit placement
With a limited number of defensive positions on the map, the key to success is careful unit placement – such as automatic crossbows facing directly down long paths – and upgrading their strength as soon as you have the cash.