For coat: Regular exercise, sweat washed/wiped off after work, good quality feeds and a balanced, healthy nutritional diet, pastured 24/7, correct regular hoof trims, teeth up to date, saddle fitted regularly and tack fitting - and good old fashioned elbow grease. Lots of grooming!
I also rug in cottons in summer (to avoid bleaching).
Nothing beats the true healthy shine that starts from within.
To keep a tail detangled, I only ONLY groom the tail when I wash it (with conditioner), or pick the knots out by hand. Don't brush it daily, it'll cause more breaks. You can plait it, bag it, wrap it, etc.. to keep it cleaner and detangled.
Mane I'm not so worried about, and gets a quick groom before each ride, as both my horses have so much mane. When I start showing, the manes will be kept short and neat.