Prepare for the next milestone, before getting into the Rush strategy.
Spend the minimum while getting the most. Not easy.
Fulfilling building milestones.
Fulfilling troop and monster milestones.
Understand the concepts at stake.
Building milestones are levels multiple of 5 (5, 10, 15, 20...) Each milestone requires blueprints. If you don't have enough blueprints, you can buy them with gold.
Buildings are the most important thing in your city. You may want to have them fully upgraded before going for the next milestone. Buildings are also a must-have, must-upgrade for troop and monster milestones.
Build one of each type, the ones you can, and upgrade them till the current building milestone minus one. This guide will not tell you how many Farm houses or Mansions you must have. Learn by experience, and start at least with two of each. The same occurs with Barracks, the more you have, the more troops you will train, the more time you will need. I would suggest starting with three and see how comfortable you are with training time and cost.
Using milestone 15 as example, your city should reach:
At least one of each type of building at level 14.
Do the Capitol the last.
At this point, buildings are prepared for the Rush strategy to the next milestone.
Troop and monster milestones are the tiers (I, II, III, IV...) You need troops to fight squads and get Valor Points. VPs are used in Academy to upgrade technologies.
You will start with tier I and confronting small squads. Do your dailies, gather VPs and don't worry about next tier. This fight happens in buildings and technologies.
Technologies are upgraded in the Academy. Some technologies upgrade what you already have, strength and health for your army, new kind of troops, exploring crypts. Others upgrade the speed to get those technologies or to upgrade your buildings. If you want to prepare for big upgrades, better invest in those technologies that will facilitate the upgrades.
The technologies that are directly related to your troops are easy to find and easy to achieve, at first. Things get complicated in higher tiers, and we will prepare them.
In the Academy you will find the Boost section, and inside the things we need to upgrade. Notice that upgrades have a limit, depending on your current building milestone. Also, we concentrate in two main properties, but the rest of the sections are also important. Upgrade as many technologies as you can, and following your criteria. This section aims to help you reach those upgrades easily.
In Academy, Boost section, Economy option, upgrade to 10/10 construction speed and research speed.
Once you have optimized the research, start upgrading technologies for your troops. Get as close as possible to the limit imposed by your current milestone. Upgrade as many technologies in the way, some are necessary, others not. Notice that fulfilling a milestone may require to upgrade 10/10 some of those you don't like or think are unnecessary. Try to do them before rushing time.
Every time you reach a building milestone, will unlock new technologies in the Boost section. Continue upgrading construction speed and research speed as they unlock.
Each time your hero increase his level, you'll get points to upgrade talents. There you can also upgrade construction speed and research speed.
At this point, you need to decide if you will spend more time gathering the world resources, or try to mitigate this with self production. If you want to be a producer, then also upgrade Iron, Stone, Wood, Silver and Food production. In the long term it pays off, but this is your decision to make.
Otherwise, if you decide to be a gatherer, the Boost section in Academy, has the option of Logistics. There you can upgrade gathering technologies.
Next, the Rush strategy.