Train for consecutive walking days
Kilimanjaro is not a one-day fitness test. Prepare your body for repeated days of walking by gradually increasing hiking time and carrying the daypack you expect to use.
Build aerobic endurance
Brisk walking, hiking, cycling, running or other aerobic work can help build the engine needed for long days at a controlled pace.
Strength and stability
Simple lower-body and core work can improve stability on long ascents and descents. Step-ups, squats, lunges and controlled hill walking are useful when appropriate for your fitness level.
Practice equipment
Use your boots, socks, poles and daypack before travelling. Small equipment problems become much more important after several hours on the trail.
Do not confuse training with acclimatisation
Good fitness improves trekking comfort, but it does not make a person immune to altitude. A sensible route duration and mountain pacing remain essential.