Ah, I know round there, you can see much of the route from the road. It's a moto cross course so is steep and, well, muddy. You probably can't walk the route in advannce but there are some footpaths that will give you a good idea of what you are letting yourself in for.
The hills for the most part are short and sweet - see if you can look at an OS map - bikehike is excellent, you can look at the google mapnext to the os map.
I find for really short steep hills the best approach is just to power up - carry on over the crest.
When faced with a long hill don't slow down, maintain effort, if you reduce effort you'll find it harder to pull it back at the top. Most hills look worse than they actually are.
If you can, from now on in do all your running over the downs. Find the hilliest routes you can - find the most challenging hills and keep at them until you can run up them.
I train on the South Downs all the time. You need to be able to run downhill as well as up. Running downhill isn't as obvious as running up hill.
To run downhill you need to let gravity take you, don't try and brake or you'll hurt your knees. Use your arms for balance.
Running off road you need to watch where you put your feet. (she says to herself) falling over can hurt, falling over while running at pace downhill through the woods can really hurt. I have the proof. 
I do a lot of hill running, hill reps, hill undualtions. It all helps you get stronger.