I have a few tips for everyone who is coming in to help with the project.
The big one is, of course, to check the spreadsheet as Layell has mentioned. I see people throwing out sprites in this thread without checking the spreadsheet. For many pokemon, we already have rough front and back sprites, and there's QC needed more than more sprites. If there is not, or you think your front and back sprites are better than the ones up there, please add them separately.
That brings me to my second word of advice. We have people that are phenomenal with creating front sprites, whether through making pixel-overs or scratching, but we have fewer people that are just as capable of making back sprites. If you decide to make a sprite, please try to make a back sprite to accompany the front. Consistency between front and back sprites is good: If another artist sprites a back sprite, people may see a jarring difference in art styles between two sprites.
Thirdly, be aware of the size and pose of your sprites. Just because an image is in pixels does not mean it fits in-game sprites. Consider:
Is Furfrou a giant of a pokemon that rivals Reshiram in size? It's a poodle, which is closer to the size of other canine pokemon.
Thankfully, sprites can be scaled down relatively easily--it's less likely that a spriter creates a sprite too small and must scale it up.
Make sure that the sprites made are in a relatively neutral pose, too! We'd like the sprites to all be animated at some point, and a dynamic pose may look unusual when it's idly moving. Compare your sprites to the ones in-game if you have concerns over likenesses to Gen. V ones. :)
I've been working primarily on the spreadsheet instead of posting material here. Tyrantrum (with help from elcheeso and Wyverii), Doublade, and Espurr are my most recent additions.
Edit: Partially ninja'd!