My Sudoku Method

I have a three-part marking system. It's all based on positional notation; any mark relevant to the presence or absence of a '1', for instance, is in the upper-left corner of the cell. Similarly, the other digits are in a grid, thusly:
1 2 3
4 5 6
7 8 9

If there are only two possible places for a '1', that corner will have a small circle.
If there are three, there will be a slash. If four or more, a dot.
If the numeral cannot be there, it's an x.
If there's nothing, I haven't gotten to that stage het.

I first scan for the obvious and fill those in. Then I go over the whole puzzle grid once for each numeral. Sometimes I just do the twosies (the little circles) first. Sometimes the twosies and threesies together. And sometimes I do the full monty, putting dots in the multifarious places.

The reason these marks evolved is that one can easily upgrade a dot to a slash, or a slash to a circle (a little messy but readable). And an X can always be placed over anything else.

Might write more later, maybe even with pictures.