I'll be re-creating this edit:
which I originally posted here on tumblr.
STEP 1: Make the animation part of your edit. The original tutorial I did for making Gifs with Photoshop is here. I desaturated my gif and put a mask similar to this one.
STEP 2: Decide what size the layout for your edit is going to be. I generally make mine approx 500x500 pixels (for tumblr). So I'm going to change the canvas size of my gif to 500x480. I'm changing my Anchor so that the blank canvas goes to the bottom.
STEP 3: Now it's time to work on the background (or still) part of your edit. Choose the screencaps that you want and figure out the layout you want them in. Crop and re-size as needed, then arrange it all in once canvas.
STEP 4: Go back to your gif and make sure you're on the first frame before adding a new layer and dragging it all the way to the bottom.
STEP 5: Copy and paste the still canvas onto that new layer. Move it to the desired spot on the canvas.
STEP 6: I'm going to make my background black, so add another layer at the bottom and fill it with color.
STEP 7: Do your colorings. For this edit, I'm going to color my gif differently, so I just do my regular coloring underneath my gif layers.
STEP 8: Now you're ready to save your edit. For tumblr, edits need to be 500K or under, so if you need to make adjustments by removing some frames, now is where I do that. Also, if you need to adjust your timing, do that now.