Rob is right about tyres.
If you do not have winter tyres, it is still eminently possible to drive your GS in the winter - you just need to take more care.
I got my GS430 on quite wide, low profile, all season tyres (245 / 40 / 18) around OK last year with snow on the floor. (Although the first time I took it up a snowy hill, it took some getting used too - I'm not used to looking through the side windows. Fortunately, I was going really slow, and there was nothing on the road).
The tips would be the same as for most cars:
1 - Do you NEED to drive? Dont make any unnecassary trips.
2 - SNOW mode is your friend - it does help
3- Be very careful with your right foot, very gentle acceleration and braking.
4 - Be very gentle with the steering