If you are going anywhere wilderness or high then:-
1. Get a good forecast for the specific area and check.
2. Repeat – forecasts change a lot in wild or high areas. Any doubt then change plans to something safer.
3. Leave proposed route and check in time with reliable individual and agree action if not checked in and or if you will update any deviation from the route.
4. Thorough check of the map to be aware of any hazards (cliffs etc) on the route and points where you could unintentialy take a wrong turn towards other hazards.
5. Descending either on bike or foot especially in poorer light can greatly reduce your ability to see even massive drops (see 4.)
Might sound a bit dramatic and not for Surrey but N.Wales, Lakes etc can be very wild if your are not careful.
6. Spend some time thinking through bad scenarios and what you might do if they happened – bad mechanical, bad weather, illness, accident etc.