I searched through all the photos I had taken the day of D's wedding (of which there were many) and found a head on photo of her bouquet. After cropping the photo, I had it printed in I think a 5 x 7 size so the details of the flowers were easy to visualize. Then I bought myself a set of pencil crayons from my local art supplies store and went to town.
My main piece of advice when you are creating a painting/drawing (or even if you are enlarging a photograph) is buy the frame first!! It can get very pricey to have anything professionally framed. One year when hubby and I were dating I made him a drawing for Christmas. It was a fairly large drawing and the cost of framing was somewhere between $100 and $200. My trick is to check out the prints section of Winners/Homesense and find the approximate size frame you would like. These prints are fairly inexpensive and almost always come framed AND matted. Therefore, if you custom design your artwork to fit in the frame you have a relatively inexpensive frame and matte!