While I was working with SQL Server 2008 IntelliSense, I realized that it was not functioning as I expected. Even after I had enabled IntelliSense it was still not opening any suggestions at all. After a while, I figured out some vital information regarding how to make sure IntelliSense smoothly works all the time without you giving any trouble.
Given below are four different ways through which you can enable IntelliSense.
1) Make sure you are connected to SQL Server 2008 Edition.
IntelliSense does not work with the previous versions of SQL Server.
2) IntelliSense should be enabled.
There are two ways to verify whether IntelliSense is enabled or not.
a) From Toolbar
b) Go to Tools >> Options >> Text Editor >> Transact-SQL >> IntelliSense
3) IntelliSense should be refreshed with the latest changes in database.
a) Press CTRL+SHIFT+R
b) Go to Edit >> IntelliSense >> Refresh Local Cache
4) Go to Tools >> Options >> Text Editor >> Transact-SQL >> General >> IntelliSense
Select Auto List Members and Check Parameter Information.
Reference : Pinal Dave (https://blog.sqlauthority.com)