As someone with 10+ years of mad success in sales/marketing/hacking growth, from my own startup to Fortune 500 level in several verticals, here's what you have to do:

1. Yeah, sometimes you just gotta cold call. Even better, show up. Ever watch the original Wall Street? Bud Fox calls Gekko every damn day. To get in front of your very first customers, you need to be doing this too. Go to where your ideal customers are and start talking with them (tangentially) about your product.

2. MAJOR CAVEAT: This first conversation should NOT be about you, product features, design, how much VC you've landed (or want to land). No 'push notifications' here guys. You should be listening to your customer, asking them about what problems you THINK they have that you THINK your product will solve. If it's not the type of product to obviously solve a problem (maybe you've not figured out what problem it solves or it's something that's more for fun), let the customer play with it and ask the customer high-value questions while they use it.

3. Here's the secret to successful sales in one sentence: it's not at ALL about you or the product. Remember that, listen, and your customers will start giving clues away about how to sell to them. If you get good at asking the right questions, it's like calling the Nintendo cheat hotline back in the day: the wins come really easily once someone tells you how to do it (I'd like to publicly apologize to my parents for the 1998 phone bill right now).

4. Always, always, always track the conversations. Every one. Even that 2 second one getting coffee this morning. Look for patterns (what worked, what didn't, similarities between cohorts at different stages in the buying cycle, what questions you asked that elicited the most helpful responses, etc). As Paul Graham says, to get your first users, you have to do things that don't scale. However, assuming you do this successfully, you'll need to rapidly build systems that do scale, so doing this extra work now will pay off like mad. Moreover, these conversations should help you find opportunities for the next iterations of your product. In the book Traction, the authors talk about doing sales and product iteration concurrently, and they're 100% right. If you do one without the other, you're going to struggle.

5. BE where your customers are. Remember when you had the hots for someone in high school? What would you do? Everyone, and I mean everyone, tries to put themselves near where this person is--maybe you sit nearby in class, or try to pass them in the hall, whatever. Same stuff with landing customers. Pretend like they're your crush, find out everything you can about their industry, their job (what they REALLY do and worry about, not just their title and organization), maybe some things they enjoy. It's okay to be a little creepy when prepping and strategizing sales--more info is better, because it helps you develop a more holistic picture of your ideal customer, and that narrows down the channels you should try to succeed. Just don't be obvious about your prep. Remember: the will to win is important, but the will to prepare is vital.

6. Sales come from emotion. One of the biggest problems I see when engineers sell is that they use language that makes sense to them and is technically correct, but makes the customers feel stupid. Metadata to you is a 'wikipedia for your most important software' to the lay person. Make sure you emphasize the BENEFITS to the potential customer--they don't actually care about the feature. If you have a sciences background, you will probably screw this up. That's okay, just keep working at it--if you are cognizant of this and work to correct it, you'll be doing sales like the sales pros in short order.

This is definitely not inclusive, and each bullet point deserves its own book, but in my experience, they'll deliver the most value for where you are at now. Write letters, send emails, show up early and late, go to where they are, and keep the conversations about THEM. Sales are based on trust and likability (and it helps, but isn't necessary, to have a best-in-class product). You can do it.

It's funny you ask this, because I'm trying to find a job leading sales/marketing/growth at a startup company (Series A or after) right now (started applying hard yesterday). Email me and I'll do a no-fee consult (email's in my profile); if anyone else in the community has questions, feel free to reach out as well. Even if you're not in my target company demographic, I believe in good karma. Good luck guys.