My son-in-law attended a church planting workshop put on by New Church Specialties. Although it was focusing on traditional churches, some of the initial preperatory steps may be very relevant for planting house churches:
1. Ask "Why are you doing this?" It's important to look for verification that God is at work and for confirmation that you are following His lead. He is, after all, the Church Planter.
2. Intercession. Church planting begins and ends with prayer.
3. Who? Look for those who have been called to join the church plant. When God is at work, those who are to be involved know it as well.
4. Core values. Begin to outline the core values of the church. In our house church setting, we repeat this process a number of times, involving everyone, as the church develops.
5. DNA and vision. We want to see outreach and reproduction set in place from the very outset. Again, however, we make this an all-church project early in the church planting process.
These are good "pre-church" steps. Most important, of course, is just following as the Spirit leads.
We are just beginning the process of possibly planting our third church. I will be posting journals as we go in order to log the process that God leads us in.