If mountain-peak climbing is your desire, it falls under a whole different category, and will require a different permit. Nepal is conservative with clothes, and your reception by locals can vary greatly on the way you dress. In view of local customs, men should try not to wear shorts, and women should avoid them altogether. For women, a skirt of mid-calf length is preferable to slacks or pants. Besides the issue of culturally sensitive dressing, it is also important for you to make sure you have appropriate clothing to meet your needs during a trek.
Good shoes are of great importance.
You will be walking for up to eight hours a day. They must be sturdy and comfortable. For higher altitude treks where you may have to tread snow for long hours, good boots are available for rent in Kathmandu. Thermal underwear can be great especially between November and February. Bring plenty of woolen and cotton socks.