i completely disagree. there wont be any jealously if one does game on only one of the girls, then the gamed girl will have nothing to be jealous about because she already has the guy. in order to make both of them jealous, u have to show intense attraction to both girls on different occasions when they are in the same environment.
more specific: one day give a red rose to one girl and another day give a white/pink rose to the other and so they'll fight over the colour of their rose is better than the others.
you could arrange separate lunch dates with each girl, make sure the other girl is eating her lunch close by and sees how u and the other girl are having a great time. can also "accidently make her spill her drink on ur trousers/pants and she'll rush to clean up the mess by rubbing ur leg - major jealousy sign.
a great way to make them jealous is when they see you doing kino/touching on both of them very intimately especially holding hands or each others sides.
you could ask them to do favours for you, e.g. ask a girl to get u a soda, return a book to the library for him, borrow their class notes to copy etc.
Im sure you can work on the other stuff like 'push pull technique", teasing, negging, rapport etc.
Hope that i have helped. happy gaming dude
