This is totally not what I came to the forums for, but I love food talk!
If I'm doing mashed potatoes with chicken, I add garlic powder, onion powder, pepper, like two to three times the recommended butter, and instead of milk, I used whipping cream. You will probably have to use a bit more than you would have to use milk, but don't add it all at once. Slowly add it until you get your mashed potatoes to the consistency that you want. Then, if you're in the mood for "Loaded Mashed Potatoes", go ahead and add some mild cheddar cheese and bacon bits. I like to add all that when I'm making Raspberry chicken, and it's great. The sweetness from the raspberry chicken goes really well with the saltiness of the bacon. And I like to make my mashed potatoes thick, so just chicken and potatoes ends up being pretty filling all on it's own.
But if you want simple mashed potatoes, honestly, the right amount of butter, salt, and pepper to taste does wonders. That is all I do for mashed potatoes when I'm making them for Thanksgiving dinner, and then you add that turkey gravy and it's great just like that. But again, whipping cream or half and half instead of milk.