Be unattractive (to mosquitoes)
Mosquitoes are remarkably well-equipped to track you down. Don't do them any favors by enhancing the chemical cues which lead them to you.
Fruit and floral-scented smells are a mosquito come-on. Unfortunately, both are pretty common in sunscreens. Look for an unscented formula, such as Aubrey Organics'
Natural Sun series or Avalon Organics
Baby Mineral Sunscreen. You can buy them online or at your local heath store.
Insects don't have great vision, but they are closely attuned to contrasts. Avoid dark clothing and you'll be less of a sitting duck.
You produce tons of lactic acid when you're exercising, so consider moving strenuous activities out of the late afternoon hours when mosquitoes are most active. It also helps to limit salty foods and those rich in potassium.