well first thing I see is that you are trying to put too much detail and if you are just starting up is very common. my suggestion is to then focus in the pear and try to make it as simple as possible. even more, first try to do the shading on a sphere so that you are not bothered with all the complexities of the shape. second, you should try to render your values more evenly. an easier exercise is to fill little swatches with a value, usually you do this with four intensities, from the blackest black you can do with your pencil to the lightest light one.