You will need to paint the unfinished wood tulips first. Start with the green at the bottom. Paint both the leaves as well as the stem in green. You will want to be sure to paint the edges. Also, note that this may require two coats of paint for complete coverage. Paint one coat, allow to dry, then add a second coat.
Then paint the top of each of your tulips. I used three colors so I paint four in each color. Again be sure to paint the sides as well for a finished look. You may need two coats of paint once again for complete coverage.
Once the paint on your tulips is completely dry, you can start assembling your wreath. Be sure to dry-fit the entire thing together before using any glue. The bottom layer should be alternating with two of the colors as shown.
Add drops of glue where the top layer will touch the bottom layer.
Then you just add the other two colors of tulips on the top, alternating colors in the same manner as the bottom layer. Be sure that each of the top tulips is on the dots of glue.
Then just let the glue dry completely before hanging on your door. You may need to add a loop of ribbon to the back for hanging as well.