How to ask a girl out?

^ Except spending time with someone you like isn't "so much unnecessary effort". For one thing, if that's not enjoyable, it's all not worth it.

Then again that doesn't seem to be the context of this thread. If the thread starter is in high school or below, I would suggest for him to drop it. It's most likely a waste of time even if he succeeds; and if it really isn't (which is not unheard of), what I say is powerless anyway. Heh.

I've seen some successful post-high school relationships, but yes, many don't work out. Anyways, tldr of this thread is go for it, ask her to go to a movie or coffee shop or puttputt golfing or something silly and lighthearted and fun. Make her laugh, but don't try too hard. Have fun, be yourself, and hope for the best.