First, you don't have to present the entire gospel in 2 minutes or less. I think Christians feel pressure to make their gospel presentation very short. When they do this, they sometimes (inadvertently) cut out some important truths. It's better to present well what you have time for than to short-change the entire presentation. For example, if I were using Gilbert's model (God, Man, Christ, Response), I would much rather do a thorough job with the first two points and then, if I'm running out of time or they have to go, make an appointment to complete the conversation.
Second, ask questions. I am familiar with many different methods for evangelism: Evangelism Explosion, The Four Spiritual Laws, The Bridge, Share Jesus Without Fear, and The Way of the Master. While I don't use any of them, I use all of them. What I mean is, I don't just stick to one model, but I have a conversation with the person I'm witnessing to. I ask them a lot of questions. I show a genuine interest in them, who they are, what they think. I'll ask them questions for as long as they want to answer. The questioning usually starts with where they are from and how they were raised, to the kinds of church experiences they've had, to their thoughts on the after-life. I try to continue asking questions (both theological and personal) until we hit a dead-end. Every time I've done this, at some point, the person will then say: tell me about you. Since I've shown a general interest in them, they now want to do the same. I just respond with: what do you want to know? And they usually will jump right to the end: what do you think about the after-life? I then usually repeat the question, making it clear that they really do want to hear my opinion. They nearly always repeat the question. So now I have an unbeliever almost begging for my testimony and the gospel. I have their ear, because I've earned it by showing an interest in them.
Third, rabbit trails are good and bad. I try to stay away from issues not central to the gospel (like speaking in tongues for example), but if they have a genuine interest in an area, again, I will show that my care is for them as an individual not just to get "my presentation" out. So if they really want to go down a rabbit trail, I'll follow them for a short time.
Fourth, ask if they understand. I try to be super-clear when presenting the gospel, so this question can be painful. Why painful? Because the person typically says either: 1) "Yes, I understand." But they really don't, or 2) "No, I don't understand ....". How do I know they really don't when they say they do?
Fifth, once they believe they understand the gospel, ask them to explain it to you. This is where you have to listen very closely for many reasons. You want to make sure that they have truly understand the central components of what you've told them. You want to look for a works-based salvation on the one hand and an easy-believism gospel on the other. Some people will describe back a gospel based on works, not because that's what you presented, but because lost people have a difficult time understanding God's grace. Others will describe an easy-believism gospel because that's all they've ever heard. Make sure you correct their misunderstanding.
This fifth point, I have found, is a missing key in most evangelism. People can answer "yes or no" questions easily. Give them a multiple choice test and they'll do fine. But ask them to explain the gospel and you'll quickly hear what they don't understand. Doing this helps them to really grasp what the gospel is AND helps us to understand what we might have said that was unclear. This part, while it can be painful to hear a mutilated gospel at time, can be so amazing as you hear an unbeliever explaining to you the gospel.
What about a response? There are many ways you can lead people in a response to the gospel and I do it differently for different people. My favorite way is the following:
1) Ask them if they believe what they've just explained.
2) If they say yes, ask them if they believe in Jesus, who the Bible declares Him to be and that He paid for their sins. Ask if they have repented (make sure you define this term).
3) If they say yes, I ask if they think they are a Christian. This gives another opportunity to clarify the gospel. If they say "no," I can then ask why. If they say "yes," then ...
4) I ask them to "pray the gospel" back to God, praising Him for what He has done for them. I don't lead them in a prayer, but I lead them to the One who saves. So they pray to God and give Him honor and praise.
Sixth, keep Christ the focus of everything. Don't be sidetracked by the pitfalls I described in earlier posts. Stay focused on the glory, wonder, and love of Christ. Show how beautiful and glorious He is and let the Holy Spirit work in their hearts to convict them of their sin and lostness. Don't be manipulative, but be loving and Christ-centered.