Welcome to WMF:)
If your product/service would either
1. clearly save him/her time
2. clearly save him/her money
direct approach would work well. The crucial point is that your product/service must and clearly do either one of the two or both, and he/she must be able to see it through very clearly.
Value differs between individuals, but some values are distinguishable universally. Much of it depends on your value proposition also. Strong value proposition can be presented in many ways. Well written copy is a must. Testimonials from respectable sources and/or clients are also effective (nothing new here).
You can become a respectable source yourself by earning a respect from the peers at a place such as WMF, or you can get your work published (industry-related). Getting your work published will add legitimacy to your product/service and enhance the value proposition.
It's difficult to say where your advertisements would be effective without knowing what kind of product/service you will be offering. If you were to fork up the money to advertise at a respected source for webmasters, such as WMF, you'd better be ready as keen webmasters' business will be hard-earned, though very worth it:)
Nuttin' but my MHO