If you are DISPLAYING the variable, use pounds:

<cfoutput>
Hi #name#
</cfoutput>

If you are working the variable, don't:

<cfset shortName = left(name,6)>

If you are using the variable in a string, you must use pounds:

<cfset fullname = "#firstname# #lastname#">

Of course, you could also write the above as:

<cfset fullname = firstname & " " & lastname>