[vizually]

1. Depending on your application, the end users can be from different target market/background. If that will be the case with your app, list down the top X markets and create a specific landing page which "talks" the language of the target market.

2. Cold-outreach, Find your ideal target customers on LinkedIn/Twitter, google them, message/email them on social media (lead finding tools) and ask for help. Be willing to offer to pay them for 10-15 minutes of their time. At least a few will help without asking for money.

3. Assuming what you are selling is described on a landing page (doesn't have to be), you can do a user test by asking questions to consumers using survey tools) the goal is find out if users understand what you are trying to sell (clarity of message, trustworthiness)

You can use tools like Survey Monkey, Google Surveys, even Facebook ads.

here are a couple of examples of a purpose-built tool for feedback called ninjafeedback:

https://ninjafeedback.com/simple-survey-tool