Apologetics is a large topic. I know. I wrote a 752 page book on it called Christian Apologetics. However, several foundational principles can equip you to interact wisely on the matter whether Christianity is true, rational, and pertinent to live. Here are a few.
1. Listen to what they think about Christianity and to what their own worldview is and why.
2. Be patient. Try not to rush in with the Gospel at a the wrong time.
3. Explain those aspects of Christianity that are pertinent in that discussion.
4. Live a life that causes people to ask you what you believe and why.
5. Know the content of the Bible.
6. Study the religions and worldviews that are most available in your situtation, so that you are ready to discuss them.
7. Whether or not you are a philosopher or professional apologist, read apologetics books regularly. All Christians are to be defenders of the faith (1 Peter 3:1`5-16).
8. Evaluate your own Christian worldview to find where it is strong and weak. Work on making the weak places stronger.
9. Pray at all times (Eph. 6:19).
10. Work with others who are apologetically engaged. Contend together for the truth.
11. Give people some appropriate literature to read, but do not throw books at people. That is a waste of money and is overly aggressive.
12. Perhaps suggest that your interlocuter read some portion of the Bible that fits with the conversation.