There are multiple access points to the Mt. Rainier National Park. Be sure to check with the park website to determine the best approach given your location and also weather conditions.
If yo are planning to visit the area for the wildflower bloom, plan ahead. Reservations for lodging and campsites are essential and usually well booked by mid-June.
The wildflower bloom at Mt. Rainier is considered one of the best in the world. Spring arrives late and the bloom usually takes place from late July into early August. Mt. Rainier also makes its own weather so that conditions on the higher elevations may vary widely from those at lower elevations.