I live near Amersham – there are few bridleways actually out of town itself, but go immediately north to Chesham and there’s a great network; east towards Chenies and there’s also a good few to choose from (and Shire Lane down towards Denham). Follow the canal up towrds Berkhamstead for a different type of terrain, and as stated, can be cobined with the Wendover area (train from Amersham – Wendover a good option when it’s wet). West Chilterns if you have transport over from Henley is superb.
Best way to start off is to join West Drayton MTB club social rides (good internet site).
Look forward to seeing you around!
Just pack some mud tyres for this time of year.