Neat picture!! Just a few thoughts, and these are simply my own observations so take them with the proverbial grain of salt...
(1) Over all the photo is in good shape. It appears to be a typical home grown snap shot so trying to turn it into a Studio posed quality one probably isnt going to work BUT that does not in anyway detract from its charm and simple elegance.
(2) The major areas to approach are tonal balance and spot removal. Accomplish the first objective with the use of Levels or Curves...think contrast...that in itself will help put some "focus" into the photo. Remove spots by either cloning or masking off the areas and applying a median filter at a setting of 1 then deselecting.
(3) Go Here:http://www.aim-dtp.net/aim/techniques/index.htm
and get the free filter "Rank Replace 8 band"...it is very useful for removing spots, mold spots on slides and so on
(4) Finally, dont get too enthuastic with sharpening. If you are using Photoshop try this: Rt. click on the background layer in your layers palette and copy the background layer. Then apply a high pass filter at a setting of 3.5 or so to the copy ( it lives under "Filters>Other> Highpass)...everything will turn grey...dont worry....now look at the top Lt. edge of the layers box and you will see the "Blending mode" dropdown menu. It will be set by default to normal. Press the arrow next to it and select either Overlay, Softlight or Hardlight from the menu...when you see which gives you the desired degree of sharpness, flatten the image. DONT try to get this photo crystal clear...it wont work. Just adjust the Tone, Remove the spots, perhaps crop and use the mildest sharpening you can....good luck...Tom