第一次见到外国人该怎么用英语打招呼?

非正式的可用hey; hi; hello; how do you do?/how are u doing?
正式的场合可以用Nice to meet u./I've long heard of your name.久仰大名/It's a great pleasure to have you here with us.很高兴能请到你/I am pleased to meet u.我很高兴见到你/I'm delighted to make your acquaintance.我很高兴与你结识.等等
认识很久不见也有很多.long time no see.（最常用的）经常见面的朋友可用 what's up,man?(朋友间的） 正式点可用Small world,isn't it?我们又见面了.