Aerial Transports
Aerial transports are very effective at what they do, transporting.. They give slow units, like skuttles and vehicles, a lot of speed, as much as some aircraft, I use these in raids to bring my units around and flank the enemy....
Defensive/Offensive Lines
Ever said screw it, and blown a hole in the ground? Thats what I do when the enemy won't sit still, I use strong units like guardians/punishers and better to dig big holes that the enemy can't cross, then take pot shots at em with long range stuff, when they try to escape send other units there...
Expansion of Defenses
Heh, I wonder how many people have seen this one? It's when I build defenses in areas that seem useless, but have some metal or something else important, I do this with planes because they are fast, and easy to group up, I ruined many games with this one, works best on hills

Defending your Defenses
Put 4-5 dragon teeth in front of a tower and see what happens, nothing touches it unless it fires up more, this one is good for rushers or people who make raids that come too fast to repair your units in time....
That's all I got for now, I don't feel like typing more, what are your strategies?