Sorry, I meant to answer this yesterday evening, but then forgot (I always just click on 'View New Posts', so if something hasn't had a reply since I last visited I tend to miss it!)
A teacher would be a good idea, as petrat said, if only for a couple of lessons to start you off correctly. But if you just want to have a go yourself, try 'First Repertoire for Descant Recorder' by Sally Adams (Faber). This seems to be an amalgamation of most of the best pieces from the First and Second Books of Descant Solos from the same publisher - now presumably discontinued - along with a sprinkling of more modern pieces. The 'First Repertoire Pieces for descant recorder', and the equivalent book for treble (Boosey and Hawkes) are also good.
There's masses of stuff on the market, so do have a good look, although it's not all of good musical quality! Once you can play reasonably competently on both F and C instruments you can think about joining your local SRP branch (Society of Recorder Players). Most branches have a meeting once a month or so to which everyone is welcome, and there are also recorder courses at all levels held in various places at various times throughout the year.