The first thing is to see what needs are not being met by current charities.
If you find a need, then get at least a couple of friends to help you so your organization can have a board of directors. Write a mission statement. It is always good to have legal help doing this. If you want to do shelter, you should have a remodel of a building in mind. If your area has a community foundation, you can run your organization through this. Otherwise you do not have to incorporate, but it is a good idea. If the amount of money is at least moderate, set up a trust through a lawyer. Sometimes it helps to have the support of the city commission.