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.