Now that is effective testimony!

I have always believed that the most effective testimony is to simply share what we have personally witnessed and experienced God do in our own lives.  That is what the beginning of 1st John seems like to me.  Simple and heartfelt "hey we were there and this is what we personally witnessed.". 

Not beating anyone over the head with the Bible and trying to talk them into accepting Jesus but just simply sharing our testimony, invite them to accept Jesus,  and then get out of the way and let the Holy Spirit go to work.

1 John 1:1-4(NKJV)

That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, concerning the Word of life—

the life was manifested, and we have seen, and bear witness, and declare to you that eternal life which was with the Father and was manifested to us—

that which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ. 

And these things we write to you that your joy may be full.

As R.C Sproul once said.  Something to the effect of "I had to learn that I was part of God's plan but I wasn't the whole plan."