First build a well on the oil field to the west of your base, don't rush to build a well on the eastern oil field, this will cause you to run out money before the first well is complete, when the first well is complete then start construction of a second well on the field to the east of your base.
Don't be tempted to build a well on the on the oil field on the western edge of the map, you are unlikely to be able to defend this successfully yet.
Wait until the second oil well is complete then build three turrets, two defending the first oil well, and another defending your second oil well.
You may experience a small attack during this phase, you should be able to chase them off using your existing tanks backed up the turrets you are given to start the game with.
Now bring up the tanks dialog and start continuous production of tanks, any mix of Leopard and Tigers should do fine. Sometime soon you may come under heavy attack, don't try and defend the outlying turrets and observation posts, they're not worth the effort, keep your tanks within your base where they will be backed up by the turrets in any battles. Move your tanks around within the base as required to see off any attacks. When you have six or seven tanks you can start to think about building another turret or two to help defend your base. Also replace any destroyed turrets, these are vital to maintaining an effective defence.
If you lose an oil well in these attacks stop tank production and rebuild it as quickly as possible, losing one well at this stage will put you in a dangerous situation, hopefully you will be able to rebuild it and your defences before further attacks. If you inflicted heavy losses on the attacking force that destroyed the well then you will probably be able to recover, if the attackers escaped with minimal loses expect them back again very soon.
Now comes the make or break stage, around this time the computer will start to build an oil well either on the field near you on the western edge of the map, or on an oil field in the north west corner. You must not let the computer establish and maintain oil wells on either of these sites, there's no problem letting the computer build the wells, as long as you destroy them before they generate any serious income. The extra income these wells can generate for the computer will give it almost certain victory.
A squad of six or seven tanks should be sufficient to attack a well on the nearby field. Before you venture further afield to the eastern edge it would be best to build a slightly stronger force as you will be fighting away from your base and more likely to encounter enemy forces on the way.
Once you've made sure there are no enemy wells on either available oil field retreat back to base. You can now either build up more defences and sit out any further attacks, whilst regularly sending a squad of tanks out to make sure the computer does not establish an oil well on either of the two available oil fields. Alternatively you can concentrate on building tanks and go for a quicker attack on the enemy base.
If you've now got a strong enough squad of tanks you can build an oil well on the nearby oil field, first send a group of tanks to the site, then build a turret or two, when completion of the turret(s) is complete build the oil well. You may choose to stop tank production whilst you do this, when the oil well is complete start tank production again.
If you are strong enough to hold this oil well for the next few minutes the game is almost won, keep checking the far oil field, it's still important the computer does not establish a base there.
By now you should have a large number of tanks, when you feel ready use all your tanks for one massed attack on the enemy base. Be careful, if you attack before you are strong enough you could lose all your tanks leaving you vulnerable to counter attack.