Step One

Open a new document, and select these two colours in your pallet (#E71AE1 and #7DA5D6).

Step Two

Using the gradient tool (G) click the top of the document and drag it down to the bottom, to get this effect:

Step Three

Now select these two colours in your pallet (#C7E718 and #29BA0C).

Step Four

Using each of the colours and the pencil tool (B) click and drag then pencil all over the page to get these effects:

Step Five

Click 'Filter' > 'Pixelate' > 'Mezzotint' > On the drop down menu which will appear, make sure you click 'short lines' > then click 'OK'.

Step Six

Click 'Filter' > 'Blur' > 'Radial Blur' > Make sure you set the options to: (Amount = 100) (Blur Method: Zoom) (Two time) or ctrl + F

Final Result

Final result should look somthing like this: