If you are planning to start a startup website development using ASP.NET here are the 6 valuable tips for rapid and cost effective development from DimeBrain.
1) Use ASP.NET MVC instead of ViewState mechanism for writing better code which are unit testing and maintenance friendly
2) Don't use 3rd party control libraries as developers have to spend more time in understanding the 3rd party APIs and debugging the bugs resulted due to misuse of the APIs.
5) Use a graphic designer as the startup has no excuse of poor design
Read more elaborated explanation of all the tips at DimeBrain