Besides checking the tutorial, keep in mind you will also need some experience on sprite editing.
Don't use the fancy editors like GiMP and Photoshop, simply use MS Paint if you have Windows to edit sprites and get the feel on how the sprites are supposed to look like based on pixel architechture and shading technique depinding on the generation you want to base. I recommend you base off Gen III architechture if you want to make a scratch, but you can do IV as well.