These are two great books on presuppositional apologetics by Michael A. Robinson. Every Christian should read them. God Does Exist, and The Necessary Existence of God. These books will not only help you to defend the faith and enable you to answer objections by unbelievers they will also challenge you to be a faithful witness for Christ.
At the end of The Necessary Existence of God Michael Robinson gives these practical suggestions on getting started with a witnessing program:
1. Pray- Ask God for a holy zeal for the lost.
2. Plan- Scratch out a specific time on your calendar to go out and evangelize.
3. Prepare- Pick up some tracts, a note pad, and a pen.
4. Partner- Call a friend in advance to go out with you.
5. Preach- Step out and go to hand out tracts in the marketplace.
6. Pray- Pray for the lost to come to Christ. Pray daily for a passion to witness to your neighbors, coworkers, store clerks, and everyone you see in your personal routine.