Having marketed to developers in the past I found that:

1) Producing quality content and examples showcasing the product's use/solving a problem are helpful. In writing that content you'll learn more about your market and what matters to them. Blogging was invaluable in helping me understand what developers needed, what they didnt, and what they responded to.

2) Clear documentation explaining how the product works. It shows that you care about your development and helps devs understand exactly how it works (which they will care about).

3) Communicate how you are either removing a pain point or removing work from their day. Most new tools are all about conveniently do X task.