These steps can be approached and mastered one at a time. By the end of it, you should be able to have a strong economy as you go from age I to III. Other aspects of gameplay matter too, such as specific builds, rushes, or tactics, but having a strong economy is the most important part.
Don't fall into any of these early game traps:
Farms go adjacent to your CC or farmstead, as close as they will go. I've seen many new players who put them a distance back. Don't do that.
Don't use women for mining.
Don't use men for food gathering.
Use women or men for woodcutting.
Cavalry are for hunting chickens or other animals. Only cavalry are good at this. Hunting is a very fast way to get food unless the animals are very far from the dropsite.
If you have berries, build a farmstead right next to them and have some women harvest the berries. It's twice as fast as farming.
Don't let your workers carry resources too far. Put the storehouse right adjacent to the trees when they chop wood. If your workers (except for hunting cavalry) are walking twice the width of a storehouse to return resources, they are walking too far.
Don't make a barracks until at least the end of age I. A lot of noobs make a barracks way too early, or even more than one. Your CC can produce enough soldiers by itself.
Don't make walls or wooden towers in age I either. Good players generally agree not to use walls, anyway, and plus in age I it's just a waste of resources that the enemy can simply walk around.
Don't start mining anything until the end of age I. You don't need it.
Practice until you can have constant production of units from your CC (Civic Center) for the first 10+ minutes. You should never let it be idle until you're in age III. That means:
You need enough food income to produce women nonstop until population 50. You can produce soldiers after that.
You need enough wood to make houses - and you need to make houses far enough ahead of time so that you don't get stopped by the population limit.
In alpha 20 at least, once you hit age III the plan should be to make lots and lots of champion units.
Practice not harvesting resources you can't spend. If you're ever thinking "I have more food than I need - but I wish I had more wood" then you need to transfer some workers from food to wood, and figure out some way to spend the food. (Actually, you probably needed to transfer the workers two minutes ago, but late is better than never). If you have 1000 of any resource in age I-II, you have way too much.
If you have extra wood, a good way to spend it is on economy upgrades. The highest priority upgrade is berry gathering, then woodcutting, then farming, then mining. You want economy upgrades as early as possible so you get the benefit for longer, except for the upgrades that are super expensive.
Adjust your typical build order so that you avoid having too much of the resource. If, last game, you had way more wood than you could spend, then this game, don't put as many workers on wood so early. And so on.
This more than anything else is the mark of skill. You know you're doing it right when you have just enough of every resource you need, exactly when you need it, and little excess.
Watch replays of good players! A lot of people don't know where replays are. From the starting screen, they are under Tools/Options. If you spectate or play a game with borg-, The_Company, or nobody___, then after the game you will have a replay of an expert. Switch to that player's perspective in the replay and follow what they do - what they build, when they build it, how many farms they make, when they get upgrades. Then try to copy them in your next game.
If you're spectating a game with good players, you can switch to the perspective of the best player and watch them as they play, instead of going to the replay.
Practice using Shift to queue up actions. For instance, don't just tell your woodcutter to make a house - tell him to make a house, then shift-click back on the tree! That way he will go back to woodcutting when he's done building the house, and he won't be idle.
Work out exactly what you will do in the first minute. This is a "build order." For every civ, you want to put the cavalry on chickens and the women on berries, and the men on wood. You also generally want your first batch of 5 women to chop wood, and the next 4-5 women to harvest berries. The order in which you make a storehouse, a farmstead, get the berry upgrade, and make your first house can vary.
Britons and Gauls can build a farmstead at the berries, build a storehouse at the wood, and research the berry upgrade. They will have plenty of time to get 75 wood and make their first house.
Most civs have houses that cost 150 wood and grant 10 population. With these you can't get the farmstead, the storehouse, and the berry upgrade all at once, and still have enough wood for your first house. You have to pick two of the three. If wood is very close to your CC, you can get the farmstead and berry upgrade, and get the storehouse later. If wood is far away, you need a storehouse, so you have to skip the berry upgrade to have enough wood for the house. With these civs you will need to use 3-4 workers to make the house once you have 150 wood, so that it will be done in time.
Iberians and Mauryans occupy a middle ground since their houses cost 75 wood but they don't have the population bonuses of Britons/Gauls. You can figure something out if you want to play these. Mauryans have an elephant, which can do the job of a storehouse or farmstead and help build houses.
Ptolemies are weird.
Batch Production. This is one of the secrets that separates the good players from the experts. borg- produces in batches of 5 almost all the time, and in batches of 10 when he has enough resources! Even a batch of 15 can be worthwhile. Batch production by 5 is 38% faster than producing single units. Batch production by 10 is 57% faster. Batch production by 15 is 72% faster.
You need more food to batch produce women this way. That means more on berries (like 10), more hunting, or earlier farms.
You need to plan houses more in advance, too, so that you have 5 or 10 population open when it's time to produce.
Don't delay more than a few seconds to make a batch. It's better to just be producing 1 unit if you don't have enough houses or food for a batch.
Use hotkeys for at least your production buildings, perhaps also other units. Select your CC and press Ctrl-1, and now you can select the CC again just by pressing 1. Your barracks can go on group 2. This helps you to keep production going smoothly even if your attention is elsewhere.
Be familiar with rushes. There are many types. The primary purpose of most rushes is to deny wood from the enemy by killing woodcutters. The best way to learn how to do rushes is to watch replays of experts who rushed effectively. I recommend not rushing until you have mastered the normal economy boom from age I to III.
Spartan Skiritai rush
Ptolemy camel archer rush
3 minute cavalry skirmisher rush
Briton slinger rush
Roman swordsmen rush
borg-'s 10-11 minute champions
Not all rushes are "effective." If the rusher killed 20 women but lost 10 cavalry and was driven away, that was probably not an effective rush, since 10 cavalry cost more than 20 women. Check the attacker's and defender's economy scores and populations afterwards to see if it really worked.