I don't claim to be the best DM'er out there, but in the last couple days I beat some DM'ers who claimed they were expert. (They couldn't have been)
Opening DM is like RM in that you need a good building pattern. This is what I do and seems to work fine.
Opening move vill 1 BE and vill 2-3 BN,BN,BN
Make 20 vills in each TC
Have a couple do housing behind your base. Don't group houses all together.
Have a couple do technology buildings like market, gov center, granary, and storage pits by TC.
Assign a group of villagers to start staking out military buildings. Don't stake really close to your base. Give yourself some room.
Assign a group of villagers to start towering.
The primary unit in DM's is the Armored Ele. Learn how to use it and kill it to survive and win.
I will always make at least ten priests. Number them and use to convert Armored Eles. Make your opponent have to make more than that one unit.
If your going with Cats, have big groups of them (20+) to be effective at all against a field full of Eles.
Get your economy leveled off between 90-110 vills and make sure you have lots on farms. Food is usually what runs out first unless you go heavy on dual seige.