In addition to learning the basics (vocab. and grammar) from books or apps like Duolingo, you can also change all your language settings to Spanish on your email, computer, cell phone, and social media. These are things you use on a daily basis and already know how to operate without even reading the toolbars or options. When you change the language, you will quickly learn new words and phrases because you will see them every day! Once you’re more comfortable with your reading skills, practice listening by watching movies and TV shows first with English subtitles, then with Spanish subtitles, then without subtitles. Listening to music in Spanish and having the song lyrics in front of you is also a great way to improve listening skills. The absolute best way to learn Spanish is by immersion, if you have the option to go abroad for some time. But even if you don’t, make sure you find listening material (or real people!) to hear as many different native speakers as possible, from all around the Hispanic world. Accents vary greatly between Spain, Mexico, Puerto Rico, Cuba, the Dominican Republic, and all of Central and South America.
Of course, when you take private tutoring lessons from a Spanish language expert, you also have the benefit of customized learning and someone to answer all of your specific questions! All in all, it depends on your unique learning style.