hey man, look like you needed some crits so ill drop some if you dont mind hmm in your last digis, you seem to use white to paint highlights , you should study color theory a bit to help you pick the right color for your hioghlights and shadow, the problem with white is that it desaturate the color under it at the same time it brightens it, the thing is that usually in real life, the light source is eaither warm or cold, the sun would not desaturate the highlight but rather add a bit of warm color into it. Same goes for the shadow, dont use pitch black to darken things, keep it for areas where no light can reach and bounce. About the tools, use brushes with 100% opacity to prevent ''muddy and petty '' brushstrokes, your wacom probably has a pressure sensitivy on it, make sure you use it to your advantage, either set the pressure on opacity or maybe on brush tip size or stuff like that, play with all those settings, download other people brushes and analyze the way they did them and try to figure out why they wanted the brush to work this way to create different effect. Your pencil are your best, thats pretty good i think because its the basic of everything, so keep doing studies and digis and have fun, hope you found what to do after highschool , as long as you keep doing stuff you will improve.
cya ! ^^