It's very simple:
Using the yellow crayon, draw some large irregularly spaced waves down the paper. Then colour in the various areas with the lighter colours, one after the other. Don’t lay them on too thick: it’s more effective if the grain or texture of the paper shows through.
Now work over the areas with the corresponding darker hues. Again, allow the lower layer to show through to some extent. Afterwards, use the darkest blue to create some shadows on the green area, and similarly dark brown on the orange-red area. That way, the colours harmonize nicely.
Put a few drops of skin oil (such as is used to prevent nappy rash in babies) on a paper towel and use it to merge the colours so that you get attractive transitions. At all stages you should leave some speckles of white.
Finally take your pointed stylus and scratch wavy lines to reveal the lower layers of colour. You can always put another layer of colour on top in places, or dab with the oil again.
Some parts of your picture will probably be more pleasing than others. Assuming the frame is smaller than the paper, you can choose the most attractive region, cut it to size, and fit it in the frame.
Be brave: experiment! Try out other colour combinations: for example, various pastel shades. Or match the colours to a picture or photo that you like. Faber-Castell oil-based pastels offer a wide range of colours to choose from. You can also try different kinds of paper.