Definitely lots of grooming. Oily sprays are usually pretty good too, but be sure not to use too much.
We feed our horses one supplement, which pretty much takes care of everything. It helps their digestion, so that they can absorb vitamins from the food better, and those vitamins make their coat nice and shinyyy =]
The supplement is called Anima Strath. Here's the website: http://www.bio-strath.ch/en/anima.html
A lot of our friends use it too now, and they all love it. I'm not sure if itll do the trick in five days, but mostly it does within a week or two.