I want a review of my text :) please...  (We nearly always require a pronoun in English).

It's the first time I'm booking that I have booked classes here in at Italki. I'm very glad and looking forward to my English classes. I think it will be very helpful and it improves my English learning. I'm thinking in of trying to learn Chinese too, but it's really difficult and I don't have any idea about how to start! lol Thank you folks!

We always think of or think about in English. We never think in as in Portuguese.

I am thinking of/about the best way to learn English.

I am thinking of taking an English class.

I am thinking about all the possible ways to improve my English.

The form "I have booked" is very common in English for talking about recent events.

I have started learning English. You have corrected my notebook entry. He has written a notebok entry.