You will arrive to La Paz, or rather to El Alto international Airport. The time of the arrival depends on the airline you will use. Representative of Bolivian experience will be waiting for you, and will take you to your hotel. You must be aware of the fact that La Paz is 3600m above sea level, and thus we recommend that you take it easy at the beginning. The altitude might give you a slight headache, you might have problems sleeping, and you should not be running around. One of the best remedies is mate de coca, legally obtainable in any restaurant.
The exact program of the first day depends on the time of your arrival. If you arrive early in the morning you will have some time to discover La Paz in a slow easy pace. (to keep the effects of the altitude at bay). If you arrive in the afternoon or in the evening you will have time to have a rest and acclimatize a little to the altitude.