1. Sound more confident. This comes from practice, understand what you need to say. For example in Tomb Raider where you talk about a new city, you say "umm" and aren't direct enough.
2. Use notes. You should clearly understand what you're going to say so that you can do it well and confidently.
3. Talk a bit faster. You want to say everything relevant in the video game in a faster pace so you can communicate more valuable information about the game while playing. This also helps viewers not get bored because there are a lot of periods of silence.