How to increase application development time?

Question

Hi,
I'm currently developing the Business Model for an Application and it takes more time than expected due to change of methodologies in each iteration. I have modified to code to fit the industry standards serveral times. However if i did this in my previouse ways of doing i would have finished this by now.
However i'm currently facing these problems when developing the Business model:
1. Is there a standard pattern of coding that i should follow:
         1. How to code the validating
         2. error handling machnism
         3. method calls
2. Are there any finished sample applications of industry standards that i can downlaod (for free) so i can follow that pattern
 
TY in advance