When you buy a drill bit set, it most likely will come in a storage case. This case will help you figure out which size bit you need to use. When drilling holes for a pilot or lead hole for a nail, find which slot in the bit case the nail will fit in. The next size down is the bit you should choose. When drilling a pilot hole for a screw, you need to choose two bits. One for the starter hole and one for the pilot hole. Find which slot in your bit storage case the screw will fit in. That is the size of bit you should use for the pilot hole. For the starter hold, use the next smaller sized bit.
Need to replace your trusty old level? You can check it for accuracy. Lay one working edge on a flat surface and check the bubble. Swap it end for end, then check the bubble again. It should be in the same position. Now try the opposite working edge. Take a reading, switch end for end, and take another reading. The bubble should be in the same position. Likewise check for plumb by holding it against a flat vertical surface.