Well word of mouth is the best way.
You speak, to one guy, he speaks to the next etc etc... Success sells, so if you doing good, just talk to people.
Bitpay boasted about the $ 1 000 000 transaction the processed for a merchant, and it got picked up by the press, and next thing, they were on radio and youtube.
If I walk into a store, I ask them, "Do you accept Bitcoins"? If they say "No" and they ask what it is, I explain in detail.
I had 2 online retailers, converted in 1 day.