As has been said by other posters, the most important thing is to know the course, this only comes with many laps, it's an incredibly complex and challenging track. I golded all events eventually, with AT and using a wheel. I am now using MT and I think it would have been easier to achieve golds on these events had I spent the time on learning to use MT up front. It goes without saying that TCS should be off, ABS should be 1 unless you have exceptional finesse with braking. Both cars don't need TCS at all, the SLS in particular has buckets of grip.
The Nordschleife has many long fast sections, and getting a proper exit from the corners preceding these is of paramount importance in reducing your lap times, you can be losing large fractions of seconds on these sections by not getting the corners leading onto them correct. Concentrate on working on these and when you've got the right line through the corners you'll find large amounts of time dropping off your sectors/laps.
I also found that after many laps corners which i'd previously thought I had pretty much got the hang of were in fact possible to take much better than i'd been managing before, this is often because the exits are narrow or off camber and getting the right line is key to carrying speed through them. I've done well over a hundred laps in total now and I still learn something every time I run it.
Finally, the wet laps are a piece of cake if you're any good at throttle control, there is so much slack in the target times. I think the Intermediate full lap is the most challenging as this one feels like there is the least amount of slack in the gold time. They are all very achievable with practice though. Once you've golded all these events you'll know the track reasonably well and hopefully will love the 'ring, it's now the only place I race online the majority of the time.
EDIT: This video of Hans Stuck is worth watching to see how your lines compare to someone who can really drive well on the ring, the commentary is useful too, if you're struggling to achieve golds i'll bet there is plenty you can learn from watching a good lap (this is actually a lap of the 24H course, but save for the final corner and the GP course it's all good stuff.
http://www.youtube.com/watch?v=Bto4E5pbKhw
Good luck to those trying to get these golded!