While the walkthrough ? contains specific information on every campaign mission this article aims at providing more general advice.
Energy management
Do not rush into a mission. Use the time to accumulate energy and build up offense/defense for the future. You will need them. On that same note - do not finish a mission too early.
Unit management
Have replacements for key units such as sensors or trucks nearby to remain operational at all times.
Set vehicles to return on medium damage, if reasonable. This will help you not to lose them. This does not apply to some special ones such as the offense sensor.
Units gather experience with every damage done and become stronger with every level-up.
Recycle your units to create new and stronger units which start with the experience of the recycled units.
Attack
Queue targets using Ctrl + click to be able to leave your units alone destroying the targets you want. This will give you time to concentrate on other things.
Usage of different weapons and systems
Attach artillery to sensors and use the sensor to guide it. Defend the sensor with other forces.
Use repair turrets as the number of repair facilities is limited. Also, structures do not benefit from vehicle armor upgrades while tanks indeed do so. <!--They also help your other units to level up. Comment by Kreuvf: Really? How does this work?-->
