Mainly what has already been said,
I mainly use Maris Piper or Desiree.
Cut them into equal size pieces.
Place into cold water with a pinch of salt and bring to boil, then cover and simmer. (15-20 mins)
When a fork can easily pierce a potato, they are done.
Drain.
Put them back into the pot, with nothing covering it for 2-3 mins.
Cover the pot for another 3 mins.
Mash the potatoes, with a masher or ricer.
Heat some single cream and add about 50ml.
Mix it through, add about 1 tbsp proper butter and salt and pepper (to taste).
Add some more single cream if desired.
taste and add more seasoning if needed.
thats it.
Oh for a really intense flavour, boil the potatoes in the skins, one cooked, let cool with no lid for about 5 mins, remove skins, then mash as above,