This one is quite short and one of the easiest ones to do. Many of the flags are near a building so you can stay inside the building while defending the flag to capture it. Engineers will be very helpful because there are a lot of enemy tanks, buggies, and enemy Heavy MG's.
First Flag - On the way to the first flag there is a Heavy MG. Once you reach the first flag, stick inside of it and defend the perimeter while you capture the flag. This one shouldn't be to difficult. If it is, have someone stay upstairs as they will be out of the line of fire.
Second Flag - The second flag has a Heavy MG on the roof and a tank that spawns in the area. Take care of the Heavy MG with a rocket and then have your engineers take out the Tank. Take cover in the building and do as you did previously, protect the perimeter and raise the flag.
Third Flag - On your way to the third flag stick to the right side. Have a engineer destroy the buggy with a rocket that appears in the center of the area on the road. Then follow the train cars up the right side to get into the building. Cover the building's doors and kill the enemies in the area. Some may need to be killed on the roof so that you can begin capturing the flag.