Train at the gym to get in overall good physical shape. While you will not need any specialized or technical skills to climb Mt. Kilimanjaro, it is important to have a strong overall body, including good cardio endurance and strong quad muscles.
Purchase high-quality trekking boots, mountaineering socks, a wool cap and gloves, and layers of polypro, moisture-wicking clothing, including thermal underwear, several layers of moisture-wicking shirts, and a wind-stopping jacket. Look for these at stores that specialize in outdoor equipment such as REI, Mountain Equipment Co-op, or EMS. Consider buying trekking poles.
Fly to Tanzania, and take a bus to Moshi, the town at the entrance to the park.
Arrange for a licensed guide at one of the many local businesses in Moshi, such as the Kilimanjaro Guides Cooperative Society, located near the park gate. You are required to climb Mt. Kilimanjaro with a licensed guide. When arranging for your guide, request to meet him or her in person before handing over any of your money to the company -- this way you will get a feel for how much English he speaks and how comfortable you feel with him. Also clarify whether the company, or you, pay the cost of your guide's expenses during the climb.
Decide whether you want to walk the Rongai route (five to six nights), the Shira route (seven nights), or the North route (eight to nine nights). Maps, photos and seasonal weather conditions will help you determine which is the best fit for you.