Battle Command!

Tap a unit's portrait to select it, then tap an open area on the field within the perimeter to drop a single soldier or vehicle. You can also tap then hold to place a group of them. Each type of unit has a preferred target that they will focus on over other enemies. Do not place your units too close together to avoid explosive damage that will hit all of them. Queue-up more soldiers and vehicles before a fight when you are full to prep yourself to begin training as soon as it is over.

When possible, place and upgrade a few Harvesters in order to produce raw materials. Maximize your storage capacity as soon as possible in order to make the most out of your resources. Spend 300 Crystals when starting the game to purchase a second Engineer Bay. This will allow you to build or upgrade two structures at once, which will save time. Obtaining a third Engineer Bay will help even more, but is cost prohibitive. Begin saving crystals during the time that you are exempt from player vs. player to purchase the resources for buildings, decreasing construction times, etc. Do not place your buildings too close together in order to avoid enemy splash damage. Create enough space for your troops and vehicles. Build and upgrade army structures to handle the proper amount of troops.

Complete missions against the CPU to accrue oil and steel. Once you earn a three star rank, you can stop grinding that particular mission.