0) Learn how to save your work (it's not quite so simple on Pixlr)
1) Strive to bring out the MOST detail you can from each of your images
Right-Clicking on the layer name or on the 3 vertical dots) area on the right of the screen brings up a very helpful screen. Use that to change transparency and blending
There are a WHOLE LOT of options under adjustments will be helpful
Only a few of the filters will be helpful
Notice that you can move the layers by dragging them above and below
2) Provide a smooth blending of all of your images
3) Try to avoid distractions
4) Artistic interpretations are fine as long as they don't conflict with the above criteria
NOTE: BE SURE TO SAVE YOUR WORK EARLY AND OFTEN TO YOUR GOOGLE DRIVE.