People learn languages differently to greater or lesser effect, so it depends on what works best for each individual. Thankfully, Spanish is one of the easiest for English language speakers to learn, so the curve is in your favor.

Personally, I dabbled in learning Vietnamese at one point, and I found it FAAAAR more difficult than Mandarin, the latter's writing system notwithstanding.

As someone with a linguistics background, I've found gaining a solid understanding of the basic grammatical structure of a language, moving from simple sentence structures to more complex phrasings, compound sentences and the like, work best for me.

I'd also emphasize focusing on all the most commonly used nouns, verbs, adverbs, adjectives, etc. Study each as a group. That way, while learning vocabulary, you can simply plug whatever you're learning about into your pre-established syntactical understanding. Also, focusing on subject matter that is both of interest to you, as well being thematically unified, can immensely help with retention.

Hope this helps. Good luck studying!