What's your favourite way of market research for a new idea?

Cold email is very underrated here IMO. Eg:

"Hi $THEIR_NAME! I'm interviewing $THEIR_POSITION's to better understand $SPECIFIC_PROBLEM_YOU_THINK_THEY_HAVE. Could I interview you for 20 minutes to talk about this? Just let me know yes/no and I'll send you some potential times."

That's a pretty vague template that will still get you most of the way. Once you have more specifics about the problem/their industry etc. you can really tailor it to them which will increase your response rate.

(And you don't need very many interview tho to start seeing trends & whether there's a real problem to be solved.)

There is no one-trick to reaching first potential customers for initial feedback. Few ways I have tried: phone interviews using M-Turk, I have walked around areas where my potential customers are likely to be and just talked to them(had a partner to take notes, or record audio). Facebook groups, reddit, cold calling or emailing. One thing I can say from experience is that If you can't figure out a channel to reach those first customers , it will be nearly impossible to build a successful business. personally i would suggest to not rely on facebook/google/etc ads initially. Use them later in growth stage.

I recommend reading The Mom Test. I worked at a company called BridgeU and witnessed the founders implement it to good effect – it recently raised a hefty Series A. The book teaches a simple way to research ideas in an unbiased way while incrementing commitment from customers.

I struggled with this myself for a long time. Asking your friends is often a bad proxy - if your idea is targeted at car owners, and most of your friends bike to work, their guess is as good as yours. Also, there's something called "interviewer bias" - your friends are likely to rate your idea much more favorably simply because they are your friends.

I run https://ideacheck.io where we automate market research - just plug in your idea, define your target group and you'll receive actionable feedback from 25, 50, or 100 people from the general population.

If your idea is focused on a very specific B2B niche, I'd agree that reaching out to people via LinkedIn or cold email is the best approach.

Good luck!

I tend to reach out to friends of friends. If there aren't enough of those, I move on to cold outreach (to strangers).

Usually a short, direct and friendly email or LinkedIn message.

I find the following message structure tends to work well (paraphrasing):

'I'm really impressed by your experience in Foo. My background is in Bar. Would you be interested in sharing your experience of Foo with me, to see if there's potential to improve Foo with Bar?'

Obviously the wording isn't optimal :)

I use online forum / discussion sites like
Reddit
Facebook groups
Twitter

and offline like meetup groups

Adwords.