There is no 1 approach, the idea though to get feedback.
Depending on the idea and your entrepreneurial spirit (or lack of), you can visit Quirky.com where a community votes and then helps you create the idea and retail it.
During startup weekend events entrepreneurs are asked to hit the streets with surveys or mock ups and get people's reactions and emails or orders, etc.
You can create Facebook page with samples and prototypes and get followers feedback and acceptance.
Of course you have Kickstarter or indiegogo and even gofundme.
If you idea is programming intensive you are better learning it than trying to find a coder who will love your idea and join with no pay. They are in super high demand. A class I took for swift for example helped me a lot. Here is the site http://mbsy.co/c6bPT
For my first ever startup it took me a year to find my first programming partner. We eventually made a good return... But the thing though is that we cut it close because others were developing the same marketing software. In entrepreneurship saved time is key.
They make learning super easy.
There are ways in which not only can you validate but have the community find your venture. Learn to code if needed, design a sample and show it in a video to them and ask for support. :) good luck.