Timing

Very sound advice from yaasshat. So continuing this trend of relating back to the original post... For the most part, it's been said already, any time is a good time. Just get your confidence up and approach... If you want to be literal, there are bad times to approach someone... 1) When they look high/drunk and they appear unstable. Like you tap their shoulder and they might bite your ear off. 2) When they are angry! It's one thing if you are a master of calming people down, esp if you are professional (literally, Ph.D. on Psych) but unless you are, don't approach a steaming hot mass of metal with a squirtgun! 3) When they are engaged in conversation with friends and this is not a social event such as a party, or you are at school/work. Like if you see a trio on the train, and think one of them is attractive... If you REALLY must talk, try to wait for them to finish their talk. Don't butt in unless you really can contribute or something. Or are a bishonen that will make all three go kyaaa 4) When they are going to the restroom. Whether they want to flee a date, apply makeup, or actually eliminate waste, you are impeding them and the more you do so, the more annoyed they will get. Don't flirt with a girl holding her stomach, mate! 5) On that note, avoid approaching a girl who is coming out of the loo! Either they will assume you were waiting for them, and you will be labeled creepy stalker pervert... Or they feel very self conscious about their appearance and possibly smell for a minute or two after using a public restroom. Heaven only knows of they walk out and a piece of toilet paper is stuck to them or a zipper is not closed. Ahhh I really tend to rant, or that I apologize... But I hope my words are helpful

Break the ice when you both are having a good time. Have them be in a good mood. Make them laugh and entertained. Something like that.

Thanks everyone