Begin by making a value scale. A strip of 140# watercolor paper about 3" x 8" will work well.
1) Paint the whole strip #9 (the lightest grey), except for a patch left white at one end.
2) Let the strip dry, then paint the whole thing #8, except for a patch of #9 and white.
3) Let it dry, then paint the whole thing #7, except for the patches of #8, #9 and white.
4) Continue getting darker by increments, always leaving a patch of the previous layer. It's OK if the steps are not perfectly even, as long as each one is darker than the last.
Don't leave white between your patches.
The rest of your homework for this week is posted below.