As the first lesson, I'd be introducing the language to the student, assuming they would be starting from scratch and have had no previous contact with Portuguese. 

Firstly, the most basic topic to be taught is the Alphabet, since the knowledge of the individual sounds of each letter is fundamental to be able to pronounce full words correctly.

Then, I'd teach a brief conversation where I'd introduce myself to the student and the student would have to learn how to respond to that and introduce themselves based on what they have just learned. (Olá / Tudo bem? / Como você está? / Meu nome é ... / Eu sou a/o...).

After that, as in every lesson, there is a section dedicated to vocabulary only, and at this point, I'd do numbers (0 - 10) and maybe colours depending on the immediate progress of the student.  

To end the lesson, I'd introduce the verb to be (ser/estar) to the student, so they can read about it on their own before the next class, and therefore will be more prepared to understand how the verbs work and then have a more efficient lesson.