Like a lets play of just me leveling with music or me talking? :/ im not very good at commentating lol. im really insececure of my voice...
There are Lets Plays and Walkthroughs where people don't talk.
If you're insecure, start blabbing. If you go back to the beginning of most famous game commentators on YouTube, they really suck. The stuff they talk about..
They barely talk too. You can do that. If you're doing a campaign, some people like you not to talk. Others do. It's hard to please everyone, so most people say "fuck it" and do what they want, so you should too.
While it is hard to make it to spotlight since there are SO MANY game commentators, start off by doing something fun
Usually when a new game is release and you get access to it, hurry and make a lets play / walkthrough series on it. It might come up first in the search results.
Also you need to expand on YouTube before moving to Twitch to have a fanbase. Make sure to become a Partner on YouTube. Look into it.
EDIT: I suggest investing on the graphical issue. You have to become so and so on Twitch inorder to have 720 P recording. But if your computer is good enough to handle good games + fraps, record it in 720p on YouTube too.
YouTube > Twitch, because your video will be there 24/7, unlike Twitch where you must record live. The chances of many people watching your show live is low, while the chances of people finding your video with a little help of advertising is much higher. Once you get the snowball rolling, it's gonna hit hard.
Best of luck
EDIT 2 : Also, you should watch other Lets Plays / Game Walkthroughs / Commentators so that you get a feel of what they talk about, how they do it, etc. Hopes this helps