To be honest, the true key is just practicing. Once you get used to using the language everyday, you start to learn naturally from reading, writing, speaking, and listening to new words. My suggestion would be either A) Writing or talking with natives daily on here(or Skype), B) I don't know where you live, but if you live in an area with many Spanish natives you could try doing what I call a "level-up" practicing with them, C) Listening to podcasts, reading news, and listening to music in Spanish(should be quite easy to find on itunes, youtube, Univision, etc.), or D) Actually studying the language, its syntax, and its grammar from books(worst option)
To be honest, I am learning Spanish in school, which taught me all the grammar forms and important vocabulary and things after 2 years, but in the last 4 months on iTalki, my Spanish level has multiplied tenfold because now I am focusing on speaking and writing and now, grammar forms have become automatic for me. Learning in context is the KEY! Good luck with your Spanish studies! Espero haberte ayudado. :D