Mountain routes may be partially equipped with, at least, abseil points in place. Guide books are essential. The best ones are recommended at appropriate points in chamonix.net. The lifts open for the summer around June 15th but the Midi lift operates year round, except for scheduled maintenance usually in November. It can get hot.
Guide books describe the orientation of the crag so plan the climb when it is in the shade.
Don't forget to take water. Valley Crags Bouldering is always a popular activity, either in its own right or as training. Our climbing wall page gives you all the information you need for the walls in the Chamonix Valley. Via Ferrata is great fun for all the family. Sports climbing on the valley crags is the best way to get started.