Waterlily

Try to make your drawing of the lily large, so that you don't have to paint as much background.  I only drew the flower at first, so that I wouldn't get the lines confused with the lines for the lily pads.

I painted the flower first, before i drew in the rest (but I forgot to take the photo).  I used lemon yellow for most of it, and cadmium yellow for a few of the petals that looked darker and warmer to me.  In hindsight, I'm not sure I like the way that looks, so it might be better to just stick with the lemon yellow for all the petals.  I painted the center orange.

I used Sap Green for the lily pads, with some Ultramarine Blue added for the darker ones.  The yellow green ones on the right were Yellow Ochre mixed with Sap Green.

I usually use orange to make shadows on a yellow object, but they looked more like green to me, so I mixed some yellow ochre with sap green and painted in the shadow shapes on the petals. 

I painted in the dark water with a black that I made from Thalo Green and Alizarin Crimson.  If you don't have these two colors, just use black - or black mixed with a little green.  

I wasn't planning to add the little pieces of twigs and dried petals, but decided at the last minute that it would make the painting more interesting, so I added a tiny bit of "stuff".  Just yellow and dark brown.  It's not necessary to do this if you would rather not.