If the suggestions listed above have been followed and the data still are formatted in a way that doesn’t take full advantage of Tableau’s functionality, then the Tableau Add-In for Reshaping Data in Excel may be used to further format the data.
The Add-In is easy to download and install. Click here for instructions on how to download and install the tool and here to download it. The instructions on the Tableau page are comprehensive and there is no need for me to repeat them here.
Ken Black at 3danim8 has a very good post on the application of Reshaper. You can read it by clicking here.