go to www.gamefaqs.com
its a good site for the those stuck but i would suggest first disable all teh AA turrets, they eat ur power with not enough gain from it, replace them with either rocket soldiers or rockets in APC if u have enough money, all the while protect ur harvester, u need the money for when ur MCV comes, power up the 2 Anti vehicle to the north and east ( up and right) since there will be a lot of vehicles coming form those positions, have all ur predators stationed in those areas too, and have ur riflemen build fox holes on teh remaining sides, power up the watchtowers too, but try to balance them out since the remaining openings are all infantry. when ever something gets hurt repair it rite away, u cant afford to rebuild too many things in this mission esspecially the defensive building since u dont have a mcv yet. I found that the fully veteran units just blew up anything that came their way. Now when teh mcv comes, load up an APC with grenadiers and bring other APC with rifles in them accompanied by at least 2 predators, send them over the bridge and take out the central nexus of the laser turrets, u'll meet up some garrisoned buildings along the way, hence the greadadiers, after that protect teh mcv back to the base and u shouldnt have much trouble after that.
Note: when u have to save the mcv, Ai starts sending flame tanks on teh top section, BE CAREFUL i didnt micromange during taht time and lost 2 predators