Being honest is a crucial its easier to talk if you are being completely honest about whatever you happen to be talking about.
Never speak from ignorance if you don't know the full story behind an event or have any factual knowledge to back yourself up don't bother commentating about it. We are on the internet and people have no issue bashing your channel as well as you for speaking before knowing all the facts.
Talk about things you wanna talk about if you wanna talk about games talk about games, or politics, or art whatever you feel comfortable with and enjoy. The more you like the subject the more passionate you can be which can appeal to an to an audience
Some more practical tips
Listen to the recording when finished. Just let it play and see what you liked, disliked, then make a verdict is it what you want or can you make it better
Last tip get to the point. If you make a video about a fifa update video that's 10 minutes long but don't actually talk about the update until the 5-6 min mark people will click off since you took to long to give them the information they need. As some one who uses youtube all day outside of videos, I can say I have done this many times.
I hope I helped a little bit and good luck