Observing the Moon: Plato
Which crater is named after a favorite children's toy? Why Plato, of course. (Play-Doh! Sorry about that. I couldn't resist.) On a more serious note, the smooth, lava-filled interior of the crater Plato is an unmistakable sign that you've pointed your telescope toward Mare Imbrium. As such, it's a good jumping-off point for locating other nearby features.
The image below shows Plato in a somewhat unusual light for most of us, since it appears to have been taken just past the last quarter phase. We tend to observe the moon primarily in the evening hours, so it's normally seen illuminated from the opposite direction.
Note the sharply-pointed shadow cast by the west wall. I've seen even more prominent spiked shadows cast from the opposite wall when the moon was just beyond first quarter phase. On one occasion, the shadow spikes extended almost completely across the crater floor. The shadows greatly accentuate the promontories along the crater walls.
While the floor of the crater may at first appear pretty bland, observers have long studied it to detect different shadings and the minute craterlets spread about. These features on the floor are so small and faint that it'll require a low angle of illumination to see them. You'll also need a telescope that offers the highest possible resolution. In my 4", I have only been able to glimpse a single small bright spot near the center, and not much more in my 10-inch.