The economy of the game shares a lot of similarity with that of real life. It is better to have 1 dollar working to make more money, then it is to have 2 dollars saved. For instance, if your running a business, it is better to invest your money in equipment to manufacture more income, then it is to have your money sitting in a bank collecting interest. Of course, its better to have your money sitting in a bank collecting interest, then it is to have your money sitting under your pillow collecting dust, for the same reason, just a matter of scale.
In the game, resources have 4 primary purposes, if your resources are not fulfilling one of these purposes then they are being wasted. If they are fulfilling the wrong purpose, then their use is not being maximized, and you will lose the game to someone who more fully maximizes their resources. The number of games lost due to a bad map are grossly insignificant in comparison to the number of games lost due to poor play. In all games, both sides made numerous mistakes, with the outcome of the game hinging on the decisions of the player. Bad maps make it harder to win, but rarely do they make it impossible. Between equal opponents, the one with the worst map will lose. Rarely do you have equal opponents, and if the one with the bad map was the better player, then often you will see he will win. The question here is not who had the worst map, but who was the better player.
The earlier you spend your resources to improve your economy, the quicker you will have more resources to spend, and the quicker you can reinvest those resources to again increase your economy. And the quicker you economy will be large enough to kill your enemy, and this game is all about the quick and the dead.
Often, people will build to much economy, and lose to a smaller economy that tooled faster and attacked. Loosely one can determine the size they can build too by the size and type of map. The smaller the map, the quicker you need to be ready to fight. One should also watch their opponents actions through achievements to determine when the opponent plans to attack.
There are many ways you can use your resources, 4 general ones are as follows/.
You can invest your resources into generating more resources, economy
You can invest your resources in your military
You can invest your resources in defensive structures
You can pool your resources to acquire the ability to respond to immediate situations.
Stone age is the simplest age to determine where you should spend your resources, while 3 comes up with dock blocking and walling the map off with barracks/houses, its rare and wont be discussed here. For the most part, Stone age is all economy.
Ask yourself this. Do you build a barracks before or after you start tooling? Unless you intend to rush with axers/clubbers, building a barracks before you started tooling is the sign that you did something wrong. You either gathered too much wood, or you didn't build enough fishing boats. Even if you don't build a barracks, if you are able to build a barracks without slowing down your production of boats/docks etc, then again, you did something wrong.
Did you prevent your peons cutting stragglers from walking back to a straggler with 0 wood, cut the zeroth wood and return back to your tc, wasting an entire trip. I would not suggest micro managing your wood cutters when you have 20 of them and the distance they walk to the pit is minimal, but when you have 6, and the distance is large to the tc, then you should, for its very doable.
When getting your first wood pit, did you time it such that the peons walking a long distance gathering wood from stragglers around your tc were sent to where you will place your pit before you got enough wood. Such that when the last peon gathering wood from a straggler arrives at the tc with the last of the 120 wood, you can have your peons cutting wood at the forest turn around and quickly build a pit. Thus greatly reducing the amount of time spent walking by your peons. Did you do this when the stragglers are close to your tc, thus wasting your time and energy, and wasting the nearby wood.
Do you spread your peons out along the edge of the forest so they don't get trapped by other peons. It is better to walk a longer distance then to not walk at all.
Did you place your granary such that the peons you need to keep peon flow walk a minimal distance, do not run into each other, and do not get stuck.
These apply only to when you dock boom.
When looking to build a dock, do you have 200 wood before you start building that dock, then you didn't send your peons out soon enough. Ideally your peons should have just arrived at the place you will build the dock when you get that 100 wood, I prefer having two peons there.
Do you have more houses then you need, and not enough wood to build boats. Did you not keep up with housing, and run out. Ideally you should stay just ahead in housing, maximizing your wood by getting out as many fishing boats as quickly as possible.
Do you just barely have enough food to produce the next peon, having the rest on wood, such that you can get the pit/dock/boats as quickly as possible.
Do you place multiple fishing boats on a fishing spot right next to your dock, minimizing travel time for the boats. This will greatly speed up tool time, the most important time in the game.
At around 4-5 minutes in the game, when your wood income is enough to supply your docks(2-3), do you send many of your peons to food. Greatly speeding up your tool time, while keeping your docks producing. Once you start tooling, do you send all your peons back to wood, relying on your 10-20 fishing boats to supply you with food, and gathering enough wood to keep your fishing boats afloat in the coming battles.
Do you spread your fishing boats out after tooling? Allowing you to concentrate on other aspects of the game, as you don't need to pay as much attention to your boats as they become idle.
Do you continue building docks along the edge of the sea, greatly shortening the distance your fishing boats travel as they use up the fish near the old docks?
The other ages.
Resource management in tool and beyond is far more complex as it involves a lot more variables. For instance, you can invest most of your resources into an offensive military stance, wall your self off, just to find your enemy has built within your walls, and is himself walled up. Thus leaving your military useless and your economy dying. This was not really a resource management mistake, the resource management mistake is allowing your military to remain useless(bring them back home or tranny them across)
Thus keeping some resources in reserve to deal with situations like above has a valid use. But having 2000 wood sitting in reserve doesn't. Most mistakes in resource management after stone involve having to much of one resource, and not enough of another. When you have 1500 food, 2400 wood, and 0 gold, and decide its time to think about ironing, you messed up, you should have started already.
Resource management involves anticipating what you will need in the future, and gearing your economy to produce it. Anticipation involves balance, do not over react to a lack of resources, and create a lack elsewhere. If you have trouble anticipating what you will need, think about the games you have played before hand that have taken the path this game is taking, what did you need in those games, what will you need in this one. If your opponent starts using elephants, should you perhaps increase your gold mining operation to produce priests in counter? If you captured the sea, and realign your economy to fight on land, when suddenly your opponent makes a big push again for the sea, did you send some more peons to wood to cover the sudden need? Certainly you have some wood saved up to deal with his sudden push for the sea, and thus have the wood to produce the boats at the start, but if you don't put more peons on wood, you will not be able to keep up. If your mass producing elephants, did you first insure you would have a massive supply of food. If your mass producing wood, do you build chariots or camels. I have too often seen someone lay down 6 stables because they had a ton of wood, only to find they are not producing anywhere near enough gold/food to make use of those 6 stables.
Above all, bear in mind, these are not questions you should ask yourself when you win, for when you win you played better then your opponent. Trying to find ways to improve when playing people you beat is hard. These are questions you should ask yourself when you lose. For it is in losing that light can be shined on the way to improve your game. So don't blame the map, a bad map is just a test to see if you are up to playing better than your opponent.