If you don't have much budget, start writing.

What problem do you solve with your app? Start writing guest posts for sites that are visited by your target audience, and make those posts about something related to your app's value proposition.

Give away lots of helpful content, and readers will learn to trust you — when you're trying to sell a service, that trust is worth its weight in gold.

Test the conversions from your posts, too: did a post about X create a huge influx of sign-ups, but a post about Y didn't do much at all? Try writing more about X to find out if it's a hot-button for your customers, or if that first article was just a fluke.

You may also want to look at your acquisition funnel to make sure you've got the best chance of capturing and converting new leads.

I've helped a lot of people launch companies on shoestring budgets, so if you'd like a hand with building your strategy, let me know. I'd be happy to share what I know.

Good luck!