Hi Ste-Martin,
This is more a topic for the detailing forum tbh. Loads of write ups on there from people far more experienced than me.
If you look at the write up that Polished Bliss did for dark Audis you won't go wrong.
I warn you now though that I spend more on detailing than I do on mods, spent £80 last week and I didn't even order my polish and wax with that order, that's another £120+!
In a nutshell
1) always wash using two bucket method
2) dry using microfibre drying towels or air blaster (got to get me one)
3) use a light clay bar to remove surface contaminants (you can do loads more steps here)
4) use a light cutting compound (menzerna is great) with a cutting pad
5) polish and wax and you should see a massive difference (as 3 above the options are endless)
I use Blackfire as recommended by Polished Bliss but heard that Blackhole is good from Slims detailing.
If you want help just pm me and I'll try to add to the above