When my father died back in the sixties I had very few photographs of him and certainly none of him when he was younger.
A few years ago my brother was going through some old boxes and sent me this photograph we figure was taken about 1938. My father worked at the railway station and this is taken just outside with a colleague. My dad is on the right.

It is in pretty rough shape but intact so I scanned it at 400 dpi
giving me a graphic aprox 1300 x 900 pixels.
(the photo is 3" x 2")

Next I used the 'Auto enhance Contrast' tool set at
Bias : Neutral
Strength : Normal
Appearance : Natural

Next came the time consuming part.
To remove scratches and blemishes I find the 'Clone Brush' is best

Zoom in to do this work and do not try to do too much at once.

With all the scratches, tears and blemishes removed it already looks a lot better.

Next page add color.