First, I soaked the paper in lukewarm water in the tub for a few minutes while I got our paint mixed, brushes and boards ready (I painted as well, but to be frank, I think A's turned out better!). Then I put the wet paper on the board and used a cloth to wipe off any 'puddles'.
It was such a great experience... Much better than our last try at temperas on the easel, in which she was easily frustrated and resulted in a huge mess. In the Waldorf way, you introduce one color at a time to the young child. I think this was key for her... she wasn't overwhelmed with choices and could really concentrate on the way the paint moved on the paper. It was just so...calm.