My main tip is ...
be prepared!
I haven't ridden the event but I have ridden most of the route at one time or another and it is
very demanding! The weather can change rapidly up there so make sure you are equipped for it.
The event website recommends a minimum gear of 39/25 but I'd say that you'd need to be pretty fit to enjoy getting up some of those climbs on that. If you are not sure what gears to use, then err on the side of caution and gear down!
I'd add a warning about some of the descents ... even in the dry without other speeding riders around, they can be pretty dodgy. In a big group in the wet - watch out!
The descent off Fleet Moss towards Hawes almost did for me. It starts off at about 15-20% but then abruptly falls away at about 25%. I didn't see it coming and took off! Flying through the air at over 30 mph with the road dropping away beneath your bike is not a fun feeling! I bounced when I landed but managed to keep control of my bike. Other riders have not been so lucky. Keep your wits about you!
Fantastic cycling countryside though - enjoy yourself!