You have $1,000 and 1 person to start with. Its kinda slow at the beginning. First, buy yourself a knife, and attack someone (preferably with only 1 troop and below you in rank) and collect cash. Once you get more cash buy more armor or a better weapon. Try to get everyone armed and you'll do better attacking.
Best defensive strategy is to buy as much as you can and have NO money left over (you aren't worth attacking if you have no money). But eventually you'll need to buy yourself some defensive armor. The more the merrier.
And that's all I really have right now. Some things that I'm pretty sure about:
Attack specialists do better damage attacking, but can't defend (ditto with the defensive specialist).
The number of troops of your opponent doesn't mean as much as you think unless they have them all armed.
Some people horde money, have like 4 troops, but all of them have superior weapons and armor, so be careful (nothing like your 30 troops doing 405 damage and their 8 troops doing 1298 damage back), so having a spy or two may be worth your while once you get a week or two into the game.
You get turns and money every hour so you can check back a couple times a day, and if you are gone a long time, jump in and buy a buncha stuff to not leave yourself a target (which may be a good strategy for the 'east coasters'... wake up early, and attack all the west coasters who have been asleep a while and collecting money).
That's all I got, but mekka and baldass_newbie have been into this longer and can probably give you some better strategies.