There are no limitations as to what you should upload for as long as you speak English in the video. You may talk about how you study to improve your English, the things that you do on your free time, your hobbies and interests, or any other things that you think that could be interesting for the students.
Here are some examples.
A video log. Compilation video of things that you like to do; interests, hobbies, or even random things. Basically, about your daily life.
Anything that could motivate and convince potential students to study English.
Informational videos about ideas that you would like to share with the viewers.
English expressions and vocabularies
Some examples of common expressions and vocabularies in English.
Your opinion on certain topics
Your opinion about interesting topics or current events.