The following are few critical guidelines to be followed in sharepoint solution development.
 
1) Switching ON and OFF the AllowUnsafeUpdates option, as and when appropriately.
2) Disposing the SPSite objects after usage.
3) Disposing the SPWeb objects after usage.
4) Avoid disposing objects derived from SPContext.
5) Try the "Using" clause - to avoid the overhead of disposing objects explicitly.
 
Recently i have blogged about these in detail in our team blog
 
Additionally, you may refer to the msdn article below