Early aggression civs

How do I properly play as civs that encourage you to go aggressive early, like Greece, Assyria, and Huns?

Every time I try playing as them, I always screw something up. Sometimes, I play my "normal" strategy, aka, build monument, workers, settlers, with a few military units to dispel barbarians, the works. When I do this though, I then realize that my window of opportunity has basically passed .

Even when I am successful in being aggressive early, what I end up with is often a mess. I get too much unhappiness, and my focus on building military units often puts me behind scientifically and production wise. I conquer a civ or too, and then I am left with huge tracts of unsettled land, with large gaps between my cities and my conquered cities that I bother keeping. It ends up being really ugly.

Also, there's diplomacy. At this point in the game, 3/4 of the remaining civs are hostile to me. And I don't appreciate Shaka lecturing me about picking on weaker civs.

I'm sorry if I as unclear, its just that going aggresive early always leaves me frustrated.

Don't let hostile civs, or that moron Shaka stop your campaign. Just keep building units, and do what you do. Your window is always open for war, but I'm not the one to help you on the details. I just know what you have to do is done.

You have to know how to play agressively. Even if you can manage beating the AI by being very polite and friendly to all, you'd never be able to appreciate all the complexity that went into designing the war aspect of the game and will be very weak at multi.

One thing I've noticed is that warmongering Civs, Attila and etc, tend to keep their cities at smaller sizes or lower population. This way when they do go on a conquering spree, they don't take as harsh a happiness penalty. For me, that's one of the main warnings to start building up my forces.
But in addition to stopping city growth for a bit, I'd say make sure you also build libraries too so you don't far as far behind.
My question to you is: why do you want to go to war so early? You should wait til your Civ is prospering and has a lot of gold, happiness, and troops. Then pick a neighbor and get your war on.
Side note: In my personal experience, I've found that if you want something, you have give up something. I'd say there are 5 focuses: science, culture, economy, military, and faith. It's impossible to juggle all five at once, and extremely difficult to juggle four. Three is more realistic and is the most that I (personally) can juggle. Notice that of the five, a Civ like Shaka usually ignores culture and faith, leaving him leeway to focus more on science (I've never seen him fall too far behind), economy (he's usually good on money), and military (Oh my God, his Military!) So pick your focuses for now and as you get better, you'll find you'll get better at juggling them.

I'd suggest you keep playing the way you normally do, which would probably have to be a tradition focus and keep patient until it becomes apparent that you have to go to war (an agressive city placement threatening to take away a tile ot three of your capitol would be a good sign) and then calculate a good timing attack with just enough of your best possible units to accomplish what you need - which ideally takes away the offending city and forces your warring opponent to concede his gold and strategic resources. Then you can look around and find a new target.

Sometimes even though I'm not planning on staying peaceful the whole game I don't find a good reason not to until nukes and it's still good enough to beat emperor. But that's rare. Usually you're forced to go to war when your much needed expansion land is being taken away.