Listen to Scars, he is correct with what he states.
You cannot game girls who know each other, you would be surprised how fast information can travel and if they find you are stating the same thing to each and every one of them (for example), they will catch onto your game, and you will loose all of them.
Remember your limit on what you can handle (Girls are time consuming unfortunately) and make sure they cannot meet each other.
I know one guy who used the same lines on 3 girls at the same school, all of them ended up falling head over heals for him... till all 3 of them met together one day, and found out he used the same lines on all of them. I don't think you want to know what happened.
Just a caution. I am not stating to NOT talk with multiple girls, but just be careful about who you talk to and what you say to each of them. Talking to a wide variety of girls will make you have the power to choose, and you won't look so desperate.