The quickest way(but not the shortest) might be to take macapagal ave. until the uniwide coastal, turn left in the street, cross roxas blvd(or is it coastal road stretch already?) go straight until N.Aquino Ave. turn left again....drive straight passing through the old Domestic airport and turn right in Andrews Ave....just follow this road and you will reach terminal 3.

I also attached a link to a general map of the area...
http://ph.pagenation.com/mnl/This+Sp...14.5198875.map