Below are some common points you can remember. List is endless but I do not want 
to make it long, so that you can remember important ones.
		
				- Use string builder for concatenation rather than string when concatenation 
huge string values.
 
				- Avoid boxing / unboxing, use generics.
 
				- Avoid writing in line SQL queries use stored procedures.
 
				- Choose your indexes (clustered and non-clustered) properly. 
 
				- Use Caching for data which will not change frequently.
 
				- In ASP.NET use output cache directive for page level caching.
 
		
		Difference between .NET 1.X,2.0,3.0, 3.5 and 4.0:-
		Below is the list of top differences between the framework versions. Please 
remember the list is much bigger than what I have put down. But for interview 
perspective I have taken top 5 in each one of them so that we can remember the 
important ones.
		
				
						
								| 
										 
												.NET 2.0
										 
								 | 
								
										 
												.NET 3.0
										 
								 | 
								
										 
												.NET 3.5
										 
								 | 
								
										 
												.NET 4.0
										 
								 | 
						
						
								| 
										 Support for 64 bit application. 
										Generics 
										SQL cache dependency  
										Master pages 
										Membership and roles 
								 | 
								
										 WCF 
										WPF 
										WWF  
										WCS ( card space) 
								 | 
								
										 LINQ 
										Ajax inbuilt 
  ADO Entity framework 
  ADO data services 
										Multi targeting 
								 | 
								
										 MEF 
  Parallel computing 
  DLR dynamic 
										Code contract 
										language runtime 
										Lazy initialization 
  Background GC
 
  
								 | 
						
				
		
		
				
		
		You can also watch the below video created by
www.questpond.com which 
demonstrates how read only read only is a runtime constant and constant is a 
compile time constant.