I'm answering with the assumption that you are going to deploy this B2B rather than B2C.
Developing traction before the fact for business or enterprise solutions can be tough - you can't presell them in the way that you can with a widget, you can't drive masses of consumer traffic to them to test messaging, or gather email signups with the same efficacy.
One technique I've deployed in the past was to develop a series of "expert focus groups" - inviting people who would be future power users / decision holders on utilizing my solution. By approaching them in this way - you've got an ask that appeals to their good nature (okay, and some ego) in asking for their help, rather than overtly asking for their business. It's a great way to develop relationships with people who can provide you amazing feedback now, and are potential customers later. I also treated them as groups - trying to foster communication amongst them. Seeing the participation of the others in the group encouraged them to be more active / responsive.
I took it a step further with a handful who I thought were key as early "hero" clients that I wanted as social proof - and after engaging them for a month or more as "advisors" (not board of advisors) - asking them what they felt was still necessary to accomplish before they would be able to say yes to purchasing (not asking for them to buy, just to advise me where the solution still needed improvement).
Some of them suggested things well outside my planned roadmap, and I thanked them for the feedback and included them as future possible features. Others provided minor tweaks or indicated things that were on the horizon from a development standpoint - and I told them that "those were amazing inputs, and that I'd include them right away." I followed up with them days or weeks later when those were implemented and asked them to re-evaluate, and when the feedback was good, asked them for the sale (finding gentle ways of reminding them that I'd closed the gap they had identified). Lastly, some said that they wouldn't add anything at all - and I'd ask them immediately to become early clients, explaining how important they were as not only customers but as someone who "understood what we were doing to the core".
I'm over-simplifying of course, their responses didn't fall neatly into three buckets, and there were other response types as well (like people immediately responding that they didn't have budget - even though that's not what I asked), but those were the three categories of responses that I focused on.
Happy to provide some tips on how to set this up for your particular circumstances. Just shoot me a message.
Good question. Big question! Here are a few quick ideas off the top of my head: sneak peeks at design; simple product demo video (a la, early Dropbox: http://www.switchvideo.com/2012/07/25/how-a-simple-video-skyrocketed-dropboxs-success/); email signup page (which you then split test! Reference: https://blog.bufferapp.com/idea-to-paying-customers-in-7-weeks-how-we-did-it); do a pre-sale at a steep discount; write Medium articles outlining the big problem and various solutions; give away free stuff; use cold emails to queue up potential clients (selling is sometimes more powerful if you don't have the product yet); comment on prominent blog posts covering the problem that your solution will, well, solve; who are the other experts in your market? Connect with them on Twitter & interact with them daily; hire a designer and create killer infographics; hire a professional writer to write a killer white paper; get letters of intent from noteworthy customers; ask lots and lots of people for advice (which often leads them to want to help you out).
Let me know if I can be of further assistance.
Strategically approach existing ecommerce stores who can benefit from your product.
Then explain the risk they are at now, and how you can close that risk for them.
If your product solves that need, your lead generation efforts will grow exponentially.
If you need more detail, or have additional questions, please reserve some time here on Clarity. You have a well-defined target audience, that will make your marketing success much easier.