I would say, think about what you're trying to brand. Is it the idea of the channel or you? If it's the channel, take something that I very distinct to it. If it's you, you should be in the picture. Nothing too complicated like the others mentioned.
Needs to be something simple, meets the eye, and sort of I guess is generalised seeing that your channel consists of "everything". Make it unique, and honestly with these types of things, you can honestly do anything with it. The power of creating your own art is you can be as creative as you like, and it's quite customisable so experiment a bit as well.
It really depends on what your channel is about... if you're vlogging then a picture of yourself would prob match it or something with your channel name. A logo of your channel name is always a good one, but those icons that are posted above are pretty good examples.