A few tips:
1) if you start losing men go to the main menu and select quick restart - that lets you skip all the intro talk stuffs and get right back into playing. Generaly speaking if you lose men its best to restart (or go to a savepoint if your not worried about the medal) since you need to keep as many men alive as you can - as you get more into the game they get more experience and become very valuble troops
2) When fighting keep an eye on the health of your troops - often the enemy will focus its attacks on one solider at a time - watch the health bars and learn to retreat your troops as soon as the go to yellow health. Pull them back from the fireline - the ai might follow, but its more likley to just start attacking another close trooper. With the retreated trooper set the medics on them to get them healed back up.
This is also true of tanks as well = when damaged pull them back. With static defences often you can take them out with attack retreat cycles (though keep an eye out for builders repairing the buildings - if they do attack and kill the builder)
3) If the fight is going bad and your on the attack "runaway" is a very valid move if you have it as an option! Retreat, heal, rebuild and attack again! If your on the defensive remember that you can shoot out of the barracks building with garrisoned men
4) In defence whilst turrets are great things a simple solider in a sandbag setup can still put down a lot of fire and take quite a bit too! Its good cheap early defence
5) Always try to keep troops in their specialist jobs - that is high soliders as soldiers high medics as medics etc... since you will get better performance out of them that way. Note that often you will have to use them for other things - troops if you come under attack, builders for quick building etc.... so don't be afriad to multitask them either.
6) When your selecting troops for a new mission in the bottom left hand corner you can change their job (sometimes limited by the mission) so always make sure you have at least one medic in your squad if you can. If your going into a mission where building (always expect building) is present make sure someone starts as a builder.
7) Always keep an eye on your objectives, both primary and secondary. Some missions will put pressure on you and you might very well want to attack the enement base head on - but if your set to defend the base then defend it.. Often triggor events might suddenly put arabs against you or reinforcements for the enemy - and if you just sent all your men on the attack...welll...
8) Tanks - when either attacking or defending always try to capture enemy vehicles. With this in mind always keep at least one or two mechanics around with a high mechanic skill. Combine this with focusing your attacks on selected enemy units as as they go into the red pause the game. Now do a few things - firstly the driver of the tank will get out and start shooting - set your gunners onto him, but any splashdamage units (gun tanks, morters etc..) set to attacking another enemy unit otherwise splash damage will kill that tank you want. Then you are on a timer til the tank burns itself apart - so push the enemy back till its safe to send in the mechanic without them being shot (sometimes you can get away sending them right into the fight and sometimes not - keep an eye on their health).
If you grab the tanks in a semi working order pull them back to get them out of the fight and give them a proper repaire - once in the yellow you can even abandon them and send the mechanic back to repair another.
Note never repair a computer controled tank (that is to say a tank with the computer control upgrade - you can tell as the unit description wil say computer controled) as the computer will take over again and start shooting - instead kill this tank.
That is all I can think of for the moment I am sure there is more!