Good question. That might be one that's better posed to the overall community for more answers, but I'll give it a shot.

I learned largely in classroom settings. So if you're still in school or see classes available, I'd recommend taking those.

It really kinda 'click'ed for me when a teacher suggested thinking throughout the day 'how could I say that in Spanish?'. So like, I'd say a sentence then translate it in my head. (This will annoy your English-speaking friends if you do it out loud.) Or read a sign then repeat what it says in Spanish. Tranlating isn't usually best practice when learning a new language, but Eng and Esp are so close it works ok a lot of time. Journaling is probably the better way, going straight from thought to target language without stopping at English, but that takes time to reach.

Not to say traditional approaches are everything. Even in advanced college classes, we never read a single Spanish-language book as part of the curriculum. I feel like behind the basics, those classes toward the end should have looked a bit more like the English literature and writing classes I took in high school, just in a different language.

If I were going to start today tho, as a self-guided learner, I'd say start with a focus on dreaming.com/spanish Work through the superbeginner/beginner stages there, then start studying grammar from whichever beginner textbook. Put vocab you come across into Anki, but don't go crazy. Once you get more comfortable, eventually use learnnatively.com to find books to read and shows to watch. (Reading is not so far off - Spanish shares a massive amount of cognates with English due to shared Greek and Latin roots. If you know your word stems, you know a lot of any romance language.)

Travel is great if you can, being in that situation really kicks your brain into realizing 'this language is important'. But not required for learning.