i've lived in Spain for 3.5 years now, and my number one regret is not becoming involved in the "local" scene sooner. Many ex-pats say that it is impossible and not worth the effort, and sure, it can be fun to be in an anglophone bubble and you'll still have a great time. But befriending locals enriches the experience so much; rather than feeling like a glorified tourist, you can actually feel a part of it all. in my experience, most spainards are pretty open and excited to share their culture! a great way to do this is by going to intercambios (language exchanges) at bars, as a lot of people want to improve their english.
other miscellaneous advice:
1) idk how old you are but many museums are free/reduced admission for those under 30. there is a thing called a youth card which allows you to go to basically any museum, for free, as much as you want. this is one of my favorite parts of living in madrid especially; spending an afternoon at the prado, soaking it all in at a languid pace, knowing you can come back whenever is magical!!
2) spanish food is commonly hated on my foreigners but i love it so much now, peak comfort food. eat as much tortilla, bravas, huevos rotos, jamon, croquettas etc. as you can. drink vermut
3) working at a school is kind of a crapshoot. i've worked in two schools; one was wonderful, the other kinda hellish. like abbooo said communication and patience are really necessary— if you need support don't be afraid to ask.
4) watch spanish films and listen to spanish music. get excited!! being familiar with at least a couple almodovar films (they're amaze) (law of desire is the best) will be surprisingly useful in conversation
5) things take longer, life is slower, when it takes over an hour to get the check at a restaurant try to avoid frustration and take things less seriously