It is only wise to hire a patent prosecution attorney to file both provisional and full utility patent. For a provisional filing, you pretty much would have to write exactly the same description as the full utility patent, except that there can be no claims in the provisional. If you left out something important in the provisional and you add it in the full utility filing, you cannot claim the priority date of the provisional on that particular aspect, which can be a do or die situation for some inventors.
In my provisional filings I would always write at least the independent claims, then write out the description just like a full utility application, to make sure I would have the full benefit of the provisional application.
