1. Cash is King
2. Get feedback early
3. Business = Trust
3.5 Design is just as important as functionality.
The first one I learned the hard way - I put off monetization in the hopes of advertising revenue picking up [See Footnote 1]. The second one I realized was probably more crucial to attract and retain evangelic customers [Footnote 2]. And the third was went my server crashed and I lost everyone's data [3]. The last I learnt a lot more recently when I launched my book: Ice Cream Startups: http://sellfy.com/p/9j2z The reason for this was explained in great length here: http://startupframework.tumblr.com/post/26696517701/design-a... and Joel's take on usability: http://www.joelonsoftware.com/articles/NotJustUsability.html Short version: Affordance is the user being able to intuitively use your software/product through it's shape/design/etc. One example is how horizontal bars on doors suggest a "push" action, and a vertical bar suggests a "pull" action. Developers, myself included, often ignore this only to eventually learn: if a product feature requires a user manual, scrap it.
--
[1] [PDF] Case study on Tivo - Freemium vs Advertising models: http://w4.stern.nyu.edu/emplibrary/ModelingTheEffectsOfAdAvo...
[2] Guy Kawaski's The Art of Being a Mensch - Chapter 11 in The Art of the Start, Richard Branson's advice on freebies: http://www.canadianbusiness.com/article/74952--good-customer... and Zappos: Delivering Happiness: http://deliveringhappiness.com on creating evangelic customers.
[3] Not everyone get's it right: http://www.geek.com/articles/geek-pick/500000-gmail-accounts...