I mean something else , than "Hey , Hi " etc
Most Helpful Girl
Don't start with hey/hi/what's up/how are you/etc. Those conversations never go anywhere and girls get 10 of those messages a day.
Don't send any generic copy/paste messages. We want a personal message; not something you're also sending to 50 other girls.
Don't be crude or perverted.
Basically, just read through her profile and send a respectful message that includes why you're interested in her specifically. If you have common interests, hobbies, or values, this is where you can talk about them. Something like "I see you like to travel. I just went to New Zealand last summer, what's your favorite place you've been? or " I'm also an avid reader. Have you read [name of your favorite book] before?"
Girls on dating sites get a ton of messages every day, so they don't have the time or patience to respond to every one they get. It's more practical to only respond to those that show promise, which is why it's good to point out any common ground you have in a first message. If you don't see any common ground on her profile but you like her picture and want to message her anyway, just ask some personal questions like "what's your favorite song" or "if you won the lottery and had to give half of your winnings to someone else, who would you give it to" etc and hope for the best.