A few tips for first time players.
1) The computers weakness seems to be air superiority. So if you have a bunch of AA Guns around your base and air units you can easily decimate him.
2) Everything requires energy including your units. So make sure you have plenty of mining stations and power plants.
3) Gold is good for upgrading units from doing research.
Other then that once you have your base secure its easy pickins.

Depending on what mode you choose (real-time -- or -- turn-based) a useful strategy would be to adopt a 'pause and play' style. What I mean by this is learning how to pause the action on the battlefield when the engagements start to become too heated and resume play to devise a counter strategy. Sounds simple enough but some players forget to halt all activities to think about their next move especially if the player chooses to play real-time mode.

Another useful strategy is learning how to use units to form defensive battle lines. A row of 4 - 8 Tanks standing their ground is extremely difficult for the computer to break through with its Tanks, or Scouts charging your front line. Even better when your row of Tanks is reinforced with Scouts to give your Tanks line-of-sight range. Try adding Assault Guns to flank your opponent while your Tanks are blowing the invaders away effortlessly! :)

Remember, the A.I. is always looking to exploit weak spots in your defenses so you may have stationed a row of Tanks, Scouts and Assault Guns to protect a Mining Station on one side of your perimeter but what about the other side where your Storage Units are located? What's protecting that area?