After you have solved who your ideal customer profile is follow the below.
Hire someone on Fiverr to scrape LinkedIn for contacts based on specific parameters or use SalesQL/Apollo to scrape LinkedIn connections and others.
unlimited b2b lead generation and linkedin lead generation
Take the LinkedIn URLs and emails from the Fiverr list and upload them to Octopuscrm.io to automate LinkedIn connections with a personal note.
Start a newsletter via beehive.com for information on your company and industry or whatever your audience will find value in reading. Take the leads from Fiverr or SalesQL and subscribe them to the newsletter.
Email the contact list to set up calls for feedback on your idea. You can automate this by using snippets via Superhuman. You can also use Gmass + SendGrid to send mass emails.
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Start a Slack channel or Discord that you invite your newsletter subscribers to
Start a Reddit thread for additional feedback from your target audience
Now that you have a community and you are building software, launch a product on product hunt and get your audience to vote and review the page