Hey man, heres my tips on how to have better commentary:
-Have a general intro: A lot of people will know who you are just by listening to your intro, so it is good to have something people can count on at the start of the video
-Ask for subs: People who aren't subscribed will see that your doing YouTube for a purpose, so they will subscribe. Besides, even if they don't, it won't hurt to ask for a like or subscription
-Stay motivated: A lot of people will speak in a monotone voice, which isn't exciting for the viewers, they are there to watch an interesting video. If you stay engaged in your own conversation, they will start to feel like they are in a conversation with you, and will stay longer, and eventually subscribe
-Keep to your subject: People who don't stay true to what they are talking about (go on about something unrelated to the video's title) will not grow, unless they are getting subscribers from another source (sub4sub). People clicked on your video to see something that would pertain to its title, so dont go off your prompt
-Keep posting: Once you continue to post more and more content on your channel, whether it's commentary, lets plays, or vlogs, your commentary and speaking skills will improve. Take major YouTubers like Pewdiepie and Markiplier. Their first videos weren't that good in the commentary department, but they stuck to it and eventually became what they are today!
-Don't quit: Pretty self-explanatory... You have to give to get, so don't expect subs
To see how I commentate, check out my videos! I hoped this helped, it took my 15 minutes, so don't let it go to waste! Anyways, I hope to see you later on my channel!
-Jonesie