Be honest first and foremost. 
I think a good first step is in exploring a commonality, a mutual interest upon which you can converse and then allow the conversation to grow organically. 
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					Originally Posted by Example
					
				 Hello, my name is Will. I was browsing through profiles when I noticed that your avid interest in botany. I've always adored working with plants and I have an organic vegetable garden that keeps me and my friends well fed. I'm hoping maybe we could swap tips and see if we have anything else in common. 
 Have a great day!
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 It's simple, demonstrates a clear shared interest, and it's unassuming and pleasant. The same introduction could work in an Orchard Supply nursery should you bump into someone interesting there.