I think the most important step in starting out homeschooling is your support system. If you can make a plan to have it in place even before you begin, you are fortunate.
For me, my faith in Christ has been my major pillar of support. Next, my husband, who is there to encourage me and to discuss homeschool issues with.
My extended family is supportive of our decision, though this is not th case for all families. As this is often the cause of a great deal of stress among families, consider holding a family meeting. If possible, explain your viewpoint to your family, and give your reasons for homeschooling. It is a difficult step, but may save trouble later on. Then also, where applicable consider telling your relatives how the may help support you in your decision. Remember at all times to keep a peaceful, non judgemental tone, but be firm in your convictions. Often extended family and grandparets do wish to be involved but are terrified that this may mean teaching your children. An explanation of what kind of support would be useful can clear the air. At all times however remember it is your choice to homeschool, even if you must do it without family support. Support may be found elsewhere.
I am also fortunate to have a dear homeschooling friend who has often shared my joys and tears. I realise that these precious people are hard to find, and pray that someone will come along your path.
When you really feel isolated, live in a small town or face criticism, Internet homeschool e-loops can be so encouraging. I'll be posting a list of these at another time.
There are also a myriad of websites for specific homeschool needs. You'll find support sites for special needs children, Christian homeschool, Preschoolers, large families, Military families and more. Use a search engine, or wait till I do a post about those!
Lastly, consider joining your local support groups. Meeting regularily with other homeschool parents can be really helpful. We can learn alot from each other, share resources, pool ideas and of course arrange outings and trips. Do you know if there is a support group near you? More about support groups later...