It's interesting to see the various takes on the subject and some wishing to keep a bike in good condition as a reason or part of reason for laying the bike up.
My take on it - with careful & thorough preperation a bike can be used year round without notable degradation to the metalwork, treat metalwork & fastners properly (acf50 waxoil even wd40 etc) & don't expect a clean sparkling bike for 4 or 5 months!
As for laying a bike up, if I do lay up a bike, I tend not to change oil beforehand (but I change it regularly anyway, I'd sooner change it before use in spring rather than having new oil stood there), then give it a decent wash, make sure the bike has a good hot run before laying up & brim with petrol, drain or run empty the carbs, spray round with wd40 to keep condensation at bay & park up.
Any maintenance is generally done over the winter.
In my experience, stuff like fuel going 'off' or gumming everything up, tyres flat spotting etc simply doesn't happen over a couple of month lay up.
If there may be mice around, DO take preventitive measures, the blighters do like chewing wiring & making nests in the airbox. No, seriously.
Before starting in Spring (and I only start if taking it for a decent run), the battery goes on charge the night before, tyres/fluids/bulbs & controls are checked & fuel pump/carbs primed (not an issue with fi).
I personally, don't like leaving batteries on trickle charge & prefer to leave them, giving one full charge before use.
As always, lots of often, conflicting opinions on it out there. Do what you feel happy with