The wise prevail through great power,
and those who have knowledge muster their strength.
Surely you need guidance to wage war,
and victory is won through many advisers. NIV Proverbs 24:5-6
In any one theological debate that you've got the chance to effectively make only one or two points which will leave any kind of lasting impact. Make that impact matter. At least, do so whenever you can. I know, you can't always choose the debate topic, but sometimes you can steer the conversation to something of more substance.
Don't debate a simple Scriptural contradiction. Nearly every time, those contradictions can be rationalized away. And if they can't, they'll just be ignored.
I advise against a debate about evolution (unless you're trying to defend teaching it in school!). For faithful believers who don't believe in evolution, their belief in the Bible is founded on other stuff. In other words, they believe in Creationism because it aligns with the Bible, not the other way around. They will surely take God's word over yours!
For the same reason as for evolution, I would advise not debating about whether or not a god exists in general, because their god is not a god, but rather the God.
It comes down to this: It doesn't matter if evolution is true or if a god exists. It does matter if the Bible is true and if God exists. At least, that is the perspective of those who put their faith in that least-read-best-selling Book.
So I would advise that, if you can, you center the debate around God and the Bible. Not loosely though. Feel out your opponent. Get a sense of their core beliefs. Then pick one or two and demonstrate to them how God or the Bible is not what they perceive it to be on those specific points. Let other "advisers" argue other points to them, or simply save them for a later debate.
Of course, that does require some strength in Scriptures to do so, but I've made that a little easier for you. ;-)
Maybe you, like most Christians ;-), have no interest in deeply studying Scripture, but you love evolution or the philosophical realm of knowing how to know if a god exists or doesn't. That's fine. Argue your strengths. But know that 1) your impact on their faith is likely limited, and 2) a similar strategy of trying to find the core for their beliefs, and addressing them specifically, will probably be the most effective strategy as well.
At least, that is my perspective based on my experience in deconversion. Your mileage may vary.