Tina R. answered 11/13/19
PhD in Communication, Flexible, Creative, Native Persian/Farsi Tutor
Salaam!
First of all, I am happy that you are learning Farsi, and bravo for doing it on your own. I know it can get challenging at times.
Regarding your question: it really depends on your learning style, but I personally think grammar and vocabulary go hand in hand. At least, that's my preferred method of teaching Farsi to those who do not speak more than two or three languages. Let me clarify what I mean by this:
If you speak a few different languages, learning the grammatical aspect of Farsi may be a good point to start from, because you will have a ground for comparison and your brain can make sense of those abstract rules by referring to the grammatical system of other languages you already know. For example, if you speak Spanish, and you want to learn the Farsi subjunctive, you won't have to wrestle too long with the concept, as they are fairly similar. On the other hand, if the only language you know is English and you want to learn the Farsi subjunctive just as an abstract concept, chances are you will get frustrated and may eventually give up.
Now, if I want to teach you the Farsi subjunctive and you tell me that you only speak English, I will not start with explaining this abstract concept to you without first warming you up with some vocabulary. We will use the vocabulary to build a story or a context first. Afterwards, I will introduce the abstract concept of "subjunctive" and will give you further examples in various real life contexts (for which we will need more vocabulary). Do you see my point? That is why my suggestion is learn them both together. Of course, you will need to prioritize which words to learn first based on the frequency of their appearance in real life contexts, but that is another topic altogether.
I hope this was helpful, va movafagh baashi!
Tina