After a lot of knitting plain rounds yesterday, this afternoon the socks are 9 inches from the tip of the heel to the needles, so it is time to start decreasing for the toe.
Sometimes it is easier to see what you need to do if you fold the socks at the tip of the heel and lay the sole of the foot flat. If you have a tracing of the outline of the foot, you can lay the sole over it to see how well it matches.
I distributed the stitches between the three needles so that 36 stitches centered on the top of the foot are on one needle and the other two hold 18 each with the center of the foot bottom between these two needles. You can try on a sock at this point if you knit half way across the needle with half the stitches and are careful not to pull out the needles. When taking off the sock, push down from the cuff, don't pull it off from the toe end. This is a good practice when you wear them too.
The toe decreasing is four stitches in a round, at either end of the top of the foot needle and at the outer end of each of the two bottom needles. Some patterns decrease every other row, then weave the ends together. Others have more elaborate schemes. What really matters is the shape of the foot. If the toes form a fairly blunt shape, you probably want start the deceasing later and stop with more stitches to weave. For a pointy toe, start sooner and taper more slowly.
Mirror your decreases, when coming onto the foot edge, knit two together and on the other side use SSK. I usually put two plain stitches between the decrease stitches.
With this number of stitches, I have usually decrease and knit 3 rounds twice, decrease and knit two rounds twice, knit and decrease every other round then decrease every round until about 1/4 of the stitches are left.
If you haven't been a believer yet for knitting both socks at once, this is when it really pays off. I do one decrease and knit around, then switch to the other sock and do the same thing again.