It is actually quite feasible to cover a large area of the territory on just a few carefully selected routes, and here is one of them - the 64K bus from Tai Po Market Station to Yuen Long. A route that takes in both the new and old of Tai Po, the lush scenery of the Lam Tsuen valley as well as the rather shambolic (but sometimes picturesque) tumbledown nature of Kam Tin's various container parks :-/
This route in particular has some well-trodden tourist spots on the way including the famous (but now rather naff) Fong Ma Po Wishing Tree, Ng Tung Chai waterfalls and Kadoorie Botanical Farm. It also has a few stops along the way where you can make a further detour if you don't fancy going all the way into Yuen Long. I've pointed them out as and when so just keep reading.The great thing about this ride is also that you can hop off at either end, go for a wander, and then return and catch the bus all the way back to your starting place. Even the most timid of visitors should have no problem wandering outside their comfort zones with such an easy trip, the only bit of thought needed is deciding which end of the route you wish to catch the bus from: Tai Po or Yuen Long. Either way is fine, the route I've described is the same, it's just that I did it from TP - YL direction.