I have been in exactly the same position a number of times over the years. One day I realised that the reason I gave up promoting them is that I never really knew how my marketing efforts were doing so it always felt a bit futile.

This actually inspired my current project, which is all about measuring the results of your marketing (http://flockmetrics.com).

I think several things are helpful here. Understanding the key benefits of your product and figuring out who will most benefit from those features.

Once you know that you need to figure out how to explain your product in a way that those people can understand how it helps them and then you need to find those people.

I personally have found once I've been through that process and can see that I have a product that will make peoples lives easier it motives me to want to get the product to those people.