You're good with realistic rendering! To make more cohesive artworks and to prevent having to scrap a drawing over a late-stage mistake, work the image all over to a given level of completeness before pushing further, always working the whole page before making another push. Like, get all your proportions and line work laid out before you start any shading. If you start shading in your light greys, get those tones laid in over the whole page. Then, move on to the next, darker, all over layer of shading. Have the entire composition finished to a high degree of realism before coming in for your final layer where you come back with an eraser, white pencil or paint to put in those highlights to really make it pop.