This task uses warm and cool colour combinations. I suggest you work on two pieces of paper at a time.
select 2-3 oil pastels/crayons that are warm or cool colours {ie red/orange/yelllow]
select another 2-3 that are the other group [ie aqua, blue, violet]
starting with one group, on a sheet of paper, make rubbings of leaves or textures [use stencils or real objects] fill up all of the page but leave some areas white paper. successful works use a range of pressures and overlay the colours not just do in sections!
repeat on the other sheet of paper with the other group of crayons.
select an opposite colour group in ink [so cool ink over warm crayon] [2-3 inks] spray these over the crayons and use a brush to blend them together. Repeat with the second sheet of paper using opposite colour group inks
Using one of your continuous line drawings, lightly redraw this filling the page. successful works use a drawing that has a long stem and large open leaves along it [see examples]
Use white paint and small brush to fill in the negative space around the plant. soften out the edge of the white to fade into the background.
Use indian ink with a skewer or calligraphy pen to redraw the continuous line drawing back over the top.