Shabir Ally is said to be the most knowledgeable Muslim today when it comes to Islam and Christianity. I would only take that knowledge from him since he is no scholars, but only a specialist in Christianity. One piece of advice he gave is when debating with a Christian evangelical all you have to quote is Jeremiah 8:8. I did this once with 3-4 missionaries who came to an MSA iftar, they had their big bibles and there were about 6-7 of them in the area of which their top 3 guys took turns on preaching to me and my friend. They got pretty frustrated when it came to Trinity, and then to put the cherry on top, I remembered this verse and I asked them to open their Bibles to this verse, even though before this I had never opened a Bible. They got excited and did so, I asked them to read it, "'How can you say, "We are wise, for we have the law of the LORD," when actually the lying pen of the scribes has handled it falsely?. They gave up, did a group huddle with their fellow missionaries and left.