How to recruit beta users for my app without sounding like an ass

Basically, how do I recruit beta users for my MVP without sounding overtly self promotional? So far, the only 2 channels that have worked for me is to talk to potential users in real life or to post about it on forums like reddit, hacker news, quora and indie hackers. People do seem to like my idea but the product is not refined yet, which is why I need feedback from users in the first place. So, I am a bit cautious about promoting an unfinished product to random strangers I meet in real life and also I am afraid that if I post about my startup too often, I will be called out as a marketing shill. Also, are there any other methods for me to get initial traction other than talking to people in real life and posting about it online?