Get yourself in shape to climb the Himalayas. This cannot be accomplished with just a few nature hikes. You need to get yourself into excellent shape prior to your arrival in Nepal, since climbing will test your abilities to their limits.
Contact one of the Nepalese mountaineering associations to get in touch with a seasoned Sherpa. Since many Sherpa earn their living by guiding climbers up and down the Himalaya, they are your best source for contacting a potential guide and helper.
Travel to Nepal to meet your Sherpa guide in person. This is a crucial step, since your life may literally depend on this individual. See if you can communicate easily and well with this man or woman, find out how many ascents he or she has made and what path they recommend for your climb.
Pay the Sherpa at least the going rate, but aim to pay a little more if you possibly can. This rate will seem relatively cheap to a Westerner, and by Western standards, it is. But keep in mind that this person is a professional and a hard worker on your behalf.
Listen to what your Sherpa guide tells you about the land and the climb. He or she has climbed these mountains and knows them intimately. Respect this person's knowledge and use it to make your climb memorable and as safe as possible.