Complex sentence: His plan was to finish in the top three or wear the yellow jersey, targeting three key stages (one of which was the 13th, over Mont Ventoux) and riding conservatively until the race reached the mountains.
Split into simpler sentences: His plan was to finish in the top three, or wear the yellow jersey at some point in the race. He targeted three key stages, one of which was the 13th, over Mont Ventoux, and planned to ride conservatively until the race reached the mountains.