The important thing is to obtain good quality medium-ground oats (rather than rolled oats) and to keep stirring it to avoid solid lumps.

Bring the water (or water and milk) to a good rolling boil, preferably in a non-stick pan. Slowly pour the oatmeal into the boiling liquid, stirring vigorously with a wooden spoon all the time. Keep stirring until it has returned to the boil again, reduce the heat, cover the pan and simmer very gently for 15 minutes, stirring frequently. Add the salt at this point and simmer and stir for a further 5/10 minutes (time depends on the quality of the oats). It should be a thick but pourable consistency. Serve hot in wooden bowls if you have them.

Traditions:
Stirring the porridge should always be clockwise (though going in different directions probably mixes more efficiently).
Porridge used to be served with separate bowls of double cream. A spoonful of porridge (in a horn spoon) was dipped into a communal bowl of cream before eating.
Porridge is eaten standing up. While some people have suggested that this is out of respect for the noble dish, it probably arose from busy farmers doing other things while eating their morning porridge - or as an aid to digestion.
While some people frown at the idea of sugar on porridge others not only approve but suggest a tot of whisky. Each to their own!
Porridge used to be poured into a "porridge drawer" and, once it had cooled, it could be cut up into slices. These were easier to carry than brittle oatcakes.