Grey and black brush pens can give a sense of depth quickly and efficiently.
Drawing other sketchers can make a scene more fancy!
Coincidentally, my friend Violeta happened to bring her kids to the garden that same morning. She took some snapshots of sketchers in action--and gave me permission to share them here. 
The black brush pen has been super useful when out sketching with the baby, because I can get interesting lines down fast while standing, rocking, or bouncing with the darling little wiggler. Here are a few quick sketches from the Samurai exhibit at the Portland Art Museum as a little bonus!
