Choose your favorite charitable aid organization and contact them about volunteer opportunities. Volunteering can take many forms from working at home helping with mailings and fundraising to actually working overseas in Tibetan communities.
For volunteer opportunities in the Dharamsala/Northern India area visit: http://www.lhasocialwork.org/volunteer.html
For volunteer opportunities in the United States use this handy widget supplied by VolunteerMatch.org
Most non-profit organizations need to keep their overhead and administrative costs as low as possible. Something simple like providing office supplies or new/used office equipment can help. Contact your favorite charitable aid organization and see what they need. Ask if their overseas locations need school supplies, clothing or other items!
Many non-profit aid organizations have sponsorship programs. These programs require that you provide each month a small amount of money which will be sent to individuals, such as monks or nuns, to help with their living expenses. There are many Tibetans both inside Tibet and in Tibetan refugee communities who are destitute, are orphans, or elderly with no relatives who depend on these programs to survive. This usually does not require a large amount of money as a dollar goes much further overseas than it does here.