Guardian Unlimited has a great write-up of a recent Internet People event on 'How to make a successful internet startup'.

I think some of the key points made are applicable to all startups:
1. A user should understand immediately what it is that your business offers, and be able to easily explain it to someone else.
2. Give customers a good, selfish, reason to use you.
3. Invest in a great product rather than great advertising and then get satisfied customers to spread the word.

There's also a great quotation from the founder of IKEA, Ingvar Kamprad:

"Only when sleeping do you make no mistakes. The fear of making mistakes is the root of bureaucracy and the enemy of evolution."