Athchomar chomakaan! Good to see another enthusiastic member here on the forum!
If you're looking for some good Dothraki learning sources, I suggest starting with the Dothraki Language Handbook, written by the creator of Dothraki, David J Peterson. It goes over the basics of grammar and gives you a nice, comprehensive guide of how to make simple yet useful sentences. After getting comfortable with conversation level Dothraki, you should move on to the Dothraki wiki and take notes on all the pages. It's all cataloged and laid out in a simple format and taking notes will be a breeze. The wiki is the best source of grammar that you'll get for Dothraki, and is the easiest to access by far!
Side note: Remember not to you memrise for grammar, since its only a source for memorizing vocab (I came very close to making that mistake when first learning Dothraki).
Also, the Dothraki dictionary app and pdf file (which you can find on the dictionary thread of this forum) to find the words that you want. They're incredibly helpful when writing anything down.
Other than that, I think you'll do well and I hope to see you stay on the forums!
Okeo shafki,
Choyosor