So, you have developed your product/web/app. I dunno what your web app/app or product is, but getting you first users is really very important. And you just have to do everything and anything that comes to mind and whatever you think will work.
So in our case, we joined various Facebook groups and Linkedin groups and shared about our web app, yes that work but not in a large scale, we got the first 13 users through it. And then we tried another idea, and got our first 673 users.
We knew we should approach users where they're mostly active, where they hangout the most, online or offline. If your users are online that'll be great, they may hangout in any forum, Reddit forums or LinkedIn groups. You must need to seek for the community for your users.
Well, this is the most hard, yet most significant part of make your first user base. You must keep in mind, while sharing about your app with your upcoming users, do not make is formal or direct.
"This app really helps you to learn Japanese, to install it click below"
If you did it like this, I can assure you that your web app or app never gonna be discovered or installed by anyone.
"Are you trying to learn Japanese, well using this app help me and my fried to learn it".
Relate with people, make them feel good and motivate them on what they're trying to achieve, and connect your app with it. Human being are more emotional than rational.
OR you can talk with admins in Webmatrices Forum, and know what is the best caption to share while approaching your targeted audience.
Do not attach any kind of ads or promotional content in your website in the initial phases, until and unless you get 1,000 users NEVER display advertisement in your web app or app. Yes, you can increase your "number of users to start attaching ads in the web/app.", you can make it 2,000 if you want.
Those are fools, who do not use analytical tools and try to market them on the web. I extremely force you to use analytical tools, for web apps you can use Google Analytics, and for Mobile Apps, Google Play Console can fulfill the requirements of an analytics tools.
Firstly, know where your targeted audience exists or hangout the most, it can be an online community or similar. Let them know about your web app in an emotional informal way. Also, keep track of things, events and clicks of users with the analytical tool you're using in your web/app. And remember NOT to attach ads on them.