Hiya,
Whichever way you want to do it is fine. Most people just use 1-2 = 1 and 3-4 = 2 for d2. Or they roll odd = 1, even = 2 on any die.
For 1d3, usually it's 1-2 = 1, 3-4 = 2, 5-6 = 3, but I've also seen 1&4 = 1, 2&5=2, and 3&6 = 3.
It really doesn't matter as long as you and the players...