The first thing you need to do is to study the Bible. If you don't know what the Bible says, contains, commands, or the primary message, you can't defend it. Simply asserting being correct will do no good. You need to internalize and memorize the core of the text to see through deception about what the Bible says and things that cannot align with the Bible. If you believe it to be true, you have to be able to understand what is false. Representing the Bible correctly is key as trying to make it say something it doesn't will make you fail every time.
Second, you can't gauge Christianity as the best of choices or the nicest of options. It is either truth, leaving all else as shortcoming at best, deception at worst, or it is yet another story. You can't defend Christianity by suggesting it is a better option. People judge better options by secular and personal standards and desire. Why be Christian when I could live for myself and determine all of my actions are justified by the eternal light of myself? The answer is the truth the Bible provides, that man is judged by God and not themselves, an impossible standard and not living nicely. We are already condemned and simultaneously justified freely by Christ. This is what makes Christianity unique and true. No one can earn heaven, which is the calling of all other religions. Hell does exist which is denied by those that refuse all religion, as the individual has no power to justify their own eternal soul. The corruption we contribute to must be paid for with blood and death. That payment was made by Christ. We are all judged by His own account freely. All that is needed is to turn to He who paid this cost and rose again, conquering death forever, and form our eternal relationship with Him.
Third, you need to study the logic of both the Bible and those that deny it. It will take time to figure out all the intricate arguments all sides have, but each will have a flaw if they are based on deception or fantasy. The truth becomes evident as you study the nature of God, of man, of other interpretations of gods and powers, and the history of the world. Studying the probability of organic formation of amino acids for example will aid your ability to understand the logic of evolution for example. They suggest with enough time, life is inevitable, but the cosmic scale makes it improbable to such a degree that it borders on the insane. Amino acids form in left- and right-hand variations, named after their chemical bond formations. The right-hand variation breaks down organic chains for protein, the needed ingredient for life as we know it. This creates a massive problem for the natural formation of life as it grows to numbers of 1 in 10^80 even as high as 1 in 10^140 with the lowest suggested being 1 in 10^30 with a little agreement with this number I can find. This is a massive number, combined with the limited chances of other planets and their limited life spans with stars collapsing and the accelerating expansion of the galaxy suggesting that there is a finite formation of new stars and planets, the logic of life forming by chance becomes impossibly improbable.
Finally, you need to be a good witness. Engaging in conversations will rarely convince anyone. Instead, focus on building a reputation that will be offering your beliefs with people knowing that you are not fighting for no reason, but doing so in love, trying to share something that means the world to you with others and become brothers in Christ, joining together in the wonderful revelation of Scripture. The goal isn't to be on top of a debate, but to reach out to people, show that the Bible does make sense, that God is real and desires a relationship with you, and you desire a relationship with them.
It is so easy to get caught up in the moment and argue pointlessly, making yourself look like a fool. I am guilty of that. I am also guilty of being a bad witness. But by returning to the Bible, you return to the correction that awaits in the pages, reminding you to let God do the work in convicting. Faith cometh by hearing and hearing by the Word of God. This means that our own actions aren't the root of changing people's minds. It is God's job. Our job is simply to show it to people. You will find it much less stressful that way.