sharpen:

1. duplicate layer by dragging layer in layers palette onto new layer icon at bottom
2. select Soft Light blending mode
3. filter top layer using High Pass and adjust to right effect
4. can change transparency of top layer to attenuate the effect

remove colour cast:

1. use eyedropper (I) to pick up the colour of an area that should be white
2. create a new layer on top
3. fill (G) layer with picked up colour, then invert (ctrl I)
4. apply Colour Dodge blending mode (or sometimes Vivid Light works well)

cycle through tools using keyboard:

1. hold Shift and press the shortcut key - the tools in the toolbox cycle through (eg shift G alternates fill and gradient fill)

remove midtone colour cast:

1. create new layer, filled with 50% grey (Edit > Fill and choose 50% grey in top selection)
2. set layer blending mode to Difference - any areas on photo that are 50% grey become black
3. create an adjustment layer for Threshold...
4. move the slider down until there are just a few small black areas
5. use the color sampler tool to select in one of these areas (probably need to zoom in first)
6. switch off the grey layer and the adjustment layer
7. create a new Levels adjustment layer
8. click the middle (grey) eyedropper tool, then click the position remembered by the color sampler tool (CAPS LOCK changes tool to target - easier)