Don't use outlines.
The aim of realist value drawing is to show the light and shadow and surface tones, creating a three-dimensional illusion. Outlines only define visible edges and don't tell us anything about light and dark. Linear drawing and value drawing are two different 'systems' of representation. Mixing up the two can be confusing, if realistic drawing is your aim.
Change your approach.
When creating a value drawing, you need to shift out of line-drawing mode, and the best way to do this is to forbid yourself to draw a line, and focus on areas of value. You might use the lightest of lines to get down the basic shapes. From there, build up the shading. Often the 'outline' will be at the join between two different values, and is created by the contrast between the light and dark area.
Use the background to define foreground objects.Pay attention to drawing the shadows and background. Use them to provide contrast. A 'halo' of shading, like a vignette around the subject, is rarely successful. Leaving the background blank can work, but remember its okay to let an edge fade into the background - don't outline.