Send me an email. Before you send it, look it over a few times and delete all the hype. Just tell me three things.
First, in a matter of fact way tell me what it is you are doing. I don't want to hear any buzzwords, just an explanation. "A world changing next generation platform for GenZ blah blah blah" - yuck. "We're making an app for ordering pizza. It's better than all the other apps out there because it's like Kayak - it meta-searches all the local pizza places near you to give you a list of prices for the options you've selected" - yay.
Second, tell me how you think I can help. "Your vision with Wikipedia inspired us to contact you and we'd love to work with you" - doesn't tell me what you want from me - yuck. "We'd love to bring you on as a board member. We have an angel investor lined up, but she feels we need someone experienced in consumer internet on our board. Also, we need introductions to venture capitalists and we've targeted 10 major pizza chains who we'd like to work with and we think you could help us get meetings at a higher level in those organizations." - yay, maybe I can help with that.
Third, tell me how it benefits me. I'm very very active in my charity work, but your startup is not a charity. (If it is, then omit this last one... but I'm already advising too many so I probably can't take on more right now!) :-) "We thought you'd enjoy meeting young entrepreneurs" - bzzzzt. I DO enjoy meeting young entrepreneurs, I do it all the time as a matter of routine at conferences and through friends and so on. But if you'd like more than a friendly pat on the back and encouragement, then treat me like a businessperson - let's find something that's mutually agreeable. "If you could join us as an advisor, we'd be able to compensate you with stock options in a quantity appropriate to our stage of development." - yay.