I may be mistaken, but I'm pretty sure the beloved Alton Brown recommends red potatoes for mashing. On the other hand, you could argue for using a combination of russets and reds. I found a recipe some years back in The Chicago Tribune for the horseradish mashed potatoes they served at Oprah's restaurant (now long gone); they used a half and half ratio and they were fantastic.
After settling on the potatoes you're going to use, you need to decide if you're going to go skins on or off. Given a choice, and assuming the spuds are relatively "eye" free, I'd go with skins on. If there are too many eyes, it's a pain to trim so I just peel the darn things.
Cut the potatoes into uniform slices about 3/4" to 1" thick. Put them into well salted cold water and let them come up to temp as the water gets to boiling. Never put raw potatoes into already boiling water. When the potatoes fall apart easily when poked with a fork, they are ready for draining.
After draining, I like to mash with an old fashioned "grid" style masher. They should be well mashed but still retain some coarseness so that you know they were once real potatoes and not some flakes in a box.
As for the milk and butter; another secret from Alton Brown: warm the milk and butter separately from the potatoes before adding. Never add cold milk or solid stick butter to hot potatoes.
Finally, the flavorings. Always start with salt and ground pepper to taste. After that, I've used everything from garlic and horseradish to mustard, caramelized leeks, and basil (not all at once, mind you).
As for gravy, I never use the stuff unless I'm at Stroud's in KC. If you're gonna harden your arteries, you might as well do it right.
Oh yeah, I like corn mixed in with my taters too. It started when I was a neurotic temperamental youth who couldn't have the different foods touching each other on the plate. My Mother insensitively overlapped my corn and spuds one day, throwing me into a tantrum. With some fast talking, she finally got me to shut up and at least try the stuff. It was a revelatory moment that changed me forever as a human being and an eater. She has made me crazy countless other times in my almost 50 years, but for the gift of not being afraid to mix foods to achieve new and exciting flavors, I say to Mom, "Thank you."