I was going to type up a blurb but Aleksandra has covered off most of what I was going to say... thank you for that :).
For me the key points are:
- Flesh out your business concept on paper
- Lean canvas until you can look at it an only have a single point in each area that resonates with you totally
- Use what ever system you like to get to a very succinct profile of your key customer. Know everything about them you possibly can
- Do up a survey*, either exactly that or something which allows you to get some solid quant and qual info from your very narrow target market/ early adopter prospects
- Survey away; assess survey with a 'black hat' on and pick your product apart as much as possible; something the survey will have helped with
Depending upon the information that comes up from getting that direct feedback, you will have a fair idea of what your next steps should be :)
Hope that helps and thanks for giving me the chance to list out points! Where would a day be without a good list? :)
Good luck with it all mate.
* for offline surveying on a portable device I quite like the functionality of Quick Tap, (http://www.quicktapsurvey.com/) but if you want to have it online, then I think Survey Gizmo (www.surveygizmo.com) gives the best value for money.