Best way to write a dynamic querry

CREATE PROCEDURE sp_getUser

@username varchar(200) = NULL

AS

DECLARE @sql nvarchar(4000)

SELECT @sql = ' SELECT [name], [address] ' + 'FROM [USERS] Where [username]= ‘

SELECT @sql = @sql + ' [username] LIKE @username'

EXEC sp_executesql @sql, N'@username varchar(200)', @username