It does depend on what you are selling, as a pricing strategy will be different for either products or services. With a product, I always felt that you take the cost price and look for 100% mark up but again, it really does depend on the item and what you think your turnover of the item might be.
In terms of services it is different again. I am a head of SEO at www.mysticsense.com where our online psychics are advised to start off with a low rate per minute, undercutting the established advisors, whilst they have no ratings or regular customers, in order to encourage people to try them out. After they gain a good set of star ratings and an excellent reputation, they can raise their prices. We do not recommend any of our psychics increase their price by more than 20% at any one time or more than once a month. Equally, when they become more established a higher price indicates quality and actually attracts customers thinking they will receive a premium service.
Overall, it is mostly a trial and error experience to see if you can hit a sweet spot with pricing and stick with it.