Here are some steps I’ve found that work to get the best from less-than-perfect photos.

1. Duplicate the layer & set top layer to overlay mode. Lower the opacity to around 5 – 20%
2. Unsharp Mask filter on the lower layer; ctrl+a, ctrl+shift+c, then ctrl+v to merge and paste in new layer
3. In Adjustments, select Threshold. Drag the slider to the left, hold shift while selecting the center of the largest area of solid white; do the reverse for black. Ok, then ctrl+z.
4. In Adjustments, Levels, you will see the points selected previously. Use the white dropper to select the white point and the black dropper to select the black point. If sliders still don’t touch the sides of the histogram, then move them manually.

Grayscale: change mode to Lab, select lightness layer in channels, go back to layers palette, then convert to grayscale