ok piece of advice number 1: dont listen to chicks about chicks. they think that they understand chicks because theyre chicks, but really, a womans playa skills boil down to the possession of boobs, and the knowledge that men want to play with them more than they want to play with the men. AND i just want to say in advance, i know that all the chicks here will be miffed by that comment and not believe me, but i dont care

AND theyll probably be annoyed that im calling htem chicks...but then, theres chicks for you
now. none of this over the top "valentines day" bullshit with dinners, cards, lockets etc etc...what a load of crap. you already have your foot in the door because you knew each other in the past, and so youre in the fast lane to getting to know her because her defences are lower as per your past association, and if you try to use the valentines day angle theres a good chance that youll fubar it all up and look like an alien amp pharm i mean a douche i mean an alien amp pharm. so use this V day to get another girls attention, in case this girl falls through...although theres a decent chance that another guy is going to make a pass at her, and so you need to make enough contact with her to get her thinking about you, and therefore subliminally block all the other rose wielding Vday mofos.
so what you need to do is wait until youre in a good mood, and then call her, with the goal being to get a good vibe happening, and then get the hell off the phone!! and let her build you up in her own mind. make sure you have an excuse for getting off the phone, and remember, no matter how sweet the convo is, get the hell off the phone while its good! cant stress that enough. as per the party, well, ask what she is doing on the weekend (casually) and then drop that you are going to a party with friends, and make it sound like youre set up to have a really good time. chances are that she will tell you about her plans for the weekend, in which case you should listen, be really positive and sound happy that she is going to ahve a good time, and then mention that you might give her a call on the weekend to say hi - then get the hell off the phone. (notice that you will not only save money on phone calls, but youll avoid the trap of talking for 4 hours, burning through all of your fun chat material and best jokes, and maybe start talking about her most recent ex, therefore shunting you into the role of the counsellor...like 90% of the guys out there, who get really frustrated...liek jerseyart. poor bastard. one day we can all buy him a russian bride, and he will finally have sex.)
then on the day, call her up earlyish in the night, and see what she is up to. if she is nearby, mention that it would be fun to meet up, and if she is a 40 minute drive from you, make out as if youre having a really really good time and get the hell off the phone! since meeting her is likely to be a drama, and you have better things (and other girls) to do.
you are now set up for the next encounter, in which case she will be looking at you through rose colored glasses, and you can sweep her off her feet and be kissing her in about 5 minutes
and if you balls it all up...its not my fault

and you should have taken her to dinner, like any good douche should