The largest volcano in the Solar System is on Mars. Olympus Mons rises 24 kilometers high and measures 550 km across. By comparison, Earth's largest volcano, Mauna Loa in Hawaii, rises 9 km high and measures 120 km across. Such large volcanoes can exist on Mars because of the low gravity and lack of surface tectonic motion. Olympus Mons is located in the northern section of the Tharsis Highlands near the northern plains. Here is a 3d topographical map of the area. Olympus Mons is in the upper left corner.
Launch from Earth during time period when Earth and Mars are close, every 2 years. Fly to the Red Planet. Land at the base of Olympus Mons then start ascent. See the South Slopes route for more detail.
Anytime is good on Mars, as long as there are no dust storms or solar flares. The best time to climb would be when Mars and Earth are close in orbit, allowing for a shorter mission which would reduce your radiation exposure. The Martian winter would be the best season for a ski descent as their is no carbon dioxide snow on the northside during the summer.
Here is a link which provides Martian Weather forecasts provided by Mars Global Surveyor. Mass Coronal Ejections, Solar Flares, Coronal Holes, and Geomagnetic Storms can be tracked at the Spaceweather. The daily Martian Weather Report is another good source. An analysis of the Seasonal Snow Depth could prove useful.
Resources must conserved carefully during an ascent. A system that recycles all fluids including pee and sweat, plus a rebreather system is highly recommended. This system must be as light as possible, and be transported to each base camp.
The Crater Rim of Olympus Mons is an interesting place. Recent global mapping by the Mars Global Surveyor has not been able to find the highest point on the crater rim. Here is an animation of the crater area. Here is an overhead shot of the crater... Here is a wide angle shot...