“Moreover, brethren, I declare to you the Gospel which I preached to you, which also you received and in which you stand, by which also you are saved, if you hold fast that word which I preached to you; unless you believed in vain. For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, and that He was buried, and that He rose again the third day according to the Scriptures, and that He was seen by Cephas, then by the twelve.” (1 Corinthians 15:1-5)
Jesus died for (because of our sins); Jesus was buried; Jesus rose, Jesus was seen.
There are many ways that can be spoken. The best way, I believe, has to do with how we live. We speak the Gospel when we live the death, burial, rising and the evidence of Jesus.
So, as we see in Acts 2, they were filled with the Spirit and began to speak the wonders of God: the Gospel. Whenever we are filled with the Spirit that will happen with us, in all its varied forms.
For instance, when we forgive, we live out the life, death, burial and rising of Jesus - it is seen in us, this Gospel.
When we release things, people, situations to the Lord we live out the life, death, burial and rising of Jesus and this Gospel is seen in us.
That, to me, is the most effective form of evangelism there can be.