The best way to spot the enemy,is to see them before they see you.
Placeing your scouts way forward and keeping them stealthy while you place your forces is key.
Advance infrantry "dismounted" the turn before you think you should because any later is usally a turn too late,whoops
Keep your tanks in a overwatch situation as covering support for the infantry until the enemy intent is clear.
Try to get some mmg's and a sniper out range of most small arms,but in good LOS to react when you get fire.
If an infranry squad gets fire,try to fire with a another unit to decrease the enemy hit chance.
Another way to spot the other guy first if you have airpoints,is turn off all bombs cannons rockets ect. except maybe MG's and do a flyover diagonaly,but not so close to give them accurate AA fire,to see whats coming,then use the heavy ordanance and arty later.