Step 1: Chop potatoes
Add lots of garlic. I generally use a handful/pound of potatoes, but I'm a big fan. You can also choose to roast your garlic separately for mashing-in later, or to grate fresh garlic into the hot potatoes to be lightly cooked during mashing. Boiling** the garlic with the potatoes is a lazy but efficient way to go.
*You can use most any type of potatoes except those waxy new potatoes. Super-starchy potatoes like Russets work well, as do varieties like Yukon Golds (shown here; they've got a buttery taste) and those awesome-looking blue/purple ones. Choose what you like, and what fits your color scheme.
**Don't worry about losing nutrients to the boiling water- these are mashed potatoes! Nobody but the pre-famine Irish get their vitamins from potatoes anyway- that's what real vegetables are for. Mashed potatoes are a delicious vehicle for butter, cream, salt, cheese, garlic, and other wonderful flavors- sort of like french fries. Don't even bother pretending they're health food, and life will be much better.
Step 2: Boil
Be careful about covering the pot- potatoes are prone to boiling over and creating a gigantic starchy mess. Setting the cover on at an angle isn't sufficient- you really need to yank it before the pot comes to a full boil.