Matthew - read this
Selling a motorbike at this time of year will be rewarded with a very poor return as most people don't like riding in the winter.
Whatever you do, you will most likely lose money on it if you sell now, so live with that.
Pump up the tyres, stand it on a piece of old carpet in the garage, Spray it with ACF 50 (not the brakes), take the battery out and charge that every 2-3 weeks.
MOT it in the spring and advertise it then. You will get your best price then, and the MOT will add value to it.
Don't tax it as you need to insure first to do that and that costs a lot of money at your age.