I get this question in various forms, but I got it again recently: "What series/ topics/ books should a church plant be teaching in the first year or two?"
First off, this is a great question. It's important because how we begin our churches sets the tone for the kind of ministry we're going to have. And nothing sets the tone like the style and content of our preaching.
Having said that, here's what I'd recommend for a young church to teach in the 1st 3 years of planting:
1. One of the Gospels – We started our church teaching the Gospel on Matthew and didn't reach anyone who wasn't a Christian. I won't bore you with our story as I told elsewhere. But when we taught the Gospel of John is when things turned around for us evangelistically. So I'd recommend the Gospel of John. It's a great book to teach for outreach and also to disciple believers as well.
2. Romans – This is 2nd book I taught and it was very grounding for our church early on. I'm getting ready to teach this again starting on Easter. Nothing will help people understand the Gospel better than an in-depth study of Romans.
3. Ephesians – I didn't teach Ephesians until 2010 and it was a game changer in our church. It's very theological and practical at the same time. My only regret in teaching Ephesians is that I couldn't start over when I was done :)
Other guys will tell you all the "cool" series stuff, but if you want a healthy church, you need to lay a good foundation.