Nope, nope and nope. A newbie should NEVER, ever try to use more shades of each color because he or she will get lost, to simply put it. In the beginning, they don't really know how pixels work and by adding even more to that, it would be like adding a fuel to a fire - not good. First of all, they should focus on learning how to use as small amount of colors as possible, 3 of each + black outline would be the best to get going. Another thing you should focus on, try to think outside the box - think of spriting as a sandbox and you are a kid with toys to play with, but in this scenario, your sandbox is an empty canvas and your toys - a pencil and colors to fill it. The point is, you CAN experiment, you can do any design you want to, try to make every item unique in its own way. Last thing i'd like to mention are pure pixel-art techniques; outline-making, shading or color-picking techniques are the ones you should focus on. To simply put it: Outline usually musn't be jagged, shading should have its lightning source clearly visible (lighter/darker elements of an item/outfit/anything) and colors can be picked in a way they convert into another color, its a technique called hue-shifting and it makes a big difference.