Yeah, I read that as they already have an artist as well, just not one used to making game assets. Well, here's my progress (this is assuming they at least have knowledge in their art program of choice ahead of time)
I suggest to ALWAYS draw the image at least twice as large as the final size. Then you can shrink them to the final size at the end. This just makes things look crisper and smoother overall. Also, a lot of times I have problems of when I shrink the file, the areas along the edge of the picture end up slightly transparent. So for a standard face set, I'll shrink the final images down to 98x98 rather than 96x96 with image size, and then crop (using canvas size) it to the 96x96 to make sure I avoid that.
Also, remember to keep your image on a transparent background and not white - if you want it to be like the default RPGmaker graphics. Otherwise, you can create whatever sort of background you want. Just make it once and copy paste it 8 times later.
I can never be bothered to remember the size of a sprite sheet properly, so once I have a file with all the 96x96 face sets together, each one on it's own layer, I use canvas size (make sure you use CANVAS SIZE and not image size here or you will do strange things) and increase the width by 400% and the height by 200%. That'll give you the right size with less memorization (yay!)
I use patterns I've made to get my grids. I've got a 96x96 pattern, so I make a new layer under everything and fill that layer with my pattern grid and then line the images up on top. (if you've got a background for your images, this is where you can copy paste it in 8 times and then line each of those up along the grid as well. Or, they might be attached to your original face image already. Whichever is easier at that point) After that you can get rid of the layer with the pattern on it, and you'll have a face-set!
Until you're confident in lining stuff up though, I would pop that face set into a new project, make an NPC that says 8 lines of dialogue and uses one face on each line and watch for any jiggles or line-up mishaps causing images to overlap others in the box, etc etc. That's the best way to spot those.
I hope that helps!