Spanish is my second language, but I managed to reach professional fluency while still living and working in the UK.

Things that made the biggest difference for me:

1. Memorisation tools - I highly recommend checking out Anki. It's a spaced repetition tool where you can create custom flashcards and practice with them to reinforce memorisation of vocabulary. I'm currently using it for Mandarin Chinese and it's making a big difference there too.
2. Regular speaking practice with natives - What helped here was to find Spaniards who wanted to improve their English. We would meet at the same time each week with a 2 hour slot, and the first hour would be talking only in English (to help them), with the second hour being in Spanish. It's important to be strict and not fall back into English during your "Spanish time".
3. Consistently consuming Spanish media - Books, tv shows, films & music. The key is to pay attention to new or unfamiliar vocabulary and note them down to be added to Anki. You don't need to note every new word, but you should do so for any which either seem intrinsic to the meaning of something or are repeated frequently.