Let’s add some depth to the image. Grab a large, soft-edged brush, pick one of the colours, and in a new layer behind the main image, click a few times to create some coloured patches. Take the opacity down to 40% and set the layer’s blending mode to Pin Light. In a new layer, select another colour and paint some more blotches, this time setting the layer’s blending mode to Satin, the distance to 33, size to 250, and the contour to Gaussian. Set the opacity to 63%.
One tool that can be really useful if used well is the Blend tool. Return to Illustrator and import your image from Photoshop to use as a guide. On a new layer use the Pen tool and create two separate wavy lines, then go to Object > Blend > Blend Options, select the specified steps and select around 70, hold Cmd/Ctrl + Alt/Opt + B and see the results.
This technique can be also be applied to shapes as well, such as the triangles. You use the same process but play about with the amount to get the desired effect. Don’t be afraid to experiment; if you need to alter anything hold Shift > Cmd/Ctrl + Alt/Opt + B to release the blend.
The illustration at this point still looks a little empty and could do with a spruce-up. Choose a few more vibrant colours from your swatches and bring a few simple shapes to life using techniques such as gradient overlays. Select the Gradient tool and customise your gradient by clicking the Gradient editor in the top left hand corner.