editing is really important.
try and cutout long periods of pretty much nothing happening (unless you are trying to go for a complete 200 episode letsplay sort of thing) and only keep the parts of those sequences wherein you are being witty.
A good example of this is
Tearofgrace, he cuts out immense parts of the games he plays simply because he either wasnt talking or he wasnt funny for that amount of time.
Another example is Birgirpal.
also make sure your mic is set in the perfect zone of, being able to hear your voice but not good enough to hear everything that is happening in your house and neighborhood. You dont need viewers hearing every single click, clack, meow, bark, siren, or old man yelling at kids. also remember if you are going to be speaking in the videos, then you must be able to carry the video. be funny, be witty, tell a story, do whatever is necessary to engage your audience and keep them listening and watching. also make sure to enunciate you words (dont over enunciate).
And finally, have fun. if it isnt fun for you, its not fun for your audience.
Edit: also, dont blatantly copy schticks from other youtubers. i didnt say not to copy things, just dont be obivous.