I just left a church because the teaching was aberrant and the members weren't working. I had a number of gripes, but foundationally I did not see that the gospel was held in high enough esteem to perform evangelism.
Here's how I discerned the proper course:
>Challenged my doctrine regarding evangelism against the scripture
>Discussed it at length with the pastor
>Asked my professor for advice
>Prayed
>Prayed with others
>Sought counsel from spiritual partner
>Talked to parents
>Waited 2 weeks
We had a meeting with the pastor and we've broken fellowship, and I'm very confident I made the right decision. Really the foundation of it is seeing the scripture as supreme in every conclusion, and being aware enough to recognize that sometimes there are several good competing arguments based in scripture.