http://map.schweizmobil.ch/?lang=en
This is your best friend. You can print maps and overlay ariel photos which is very handy for scoping singletrack.
You will be very well located for some amazing riding locations. Study those maps and ride the small dashed lines at RDN and you’ll find some real treats. Some of the best stuff is not marked on there though. RDN is cool because it takes you from loose, rocky exposed hair pins to hard bed rock to leafy steeper forest singletrack all in one run. Its quite technical in places but not too hard. Train runs every hour and if you really pin it (and no punctures) you can make it down in less than an hour to meet the train, otherwise a nice beer break by the lake.
You also have Bex which is down the valley a bit but easy by train I think. Also train access to the top, but be warned, its VERY steep here. Not so technical but continous, leafy, beautiful, loamy, hang-off-the-back steepness. Dorenaz is further down the valley but it only has one track which is fun but quite brutal on the body, even on a DH bike. Its not so steep but rocky as hell.
For more xc there is plenty around Bulle/RDN area and there is riding around Leysin but I’ve never been there.
What bike will you be riding and what kind of level are you?