Do not wait for the protection to expire before attacking. Begin attacking immediately when you have the Barracks and 18 soldiers trained in order to get resources and build your base faster.
To gain access to new troops, research them in the Command Bunker after you have enough resources. Research requires a lot of time, but can be done at the same time as an upgrade.
When selecting an opponent, choose ones that have a small number of medals since they usually will be easy to defeat. While early in the game, focus on getting more resources and not medals.Upgrading tips
Upgrade the Command Bunker as soon as possible in order to unlock new buildings as well as to allow you to have more resources. Also, upgrade Factories early to maximize resource production.
Do not fortify your buildings when first starting. First, upgrade your buildings to maximum capacity, research new troops, and clear the land. After your base has been established, begin to fortify the buildings, starting with the Supply Depot and Command Bunker.