If you haven't read my advice on how to improve your English fast, do that now.
Then take a look at these essential English learning resources:
Reading Materials
https://www.cambridge.org/us/cambridgeenglish/catalog/readers/cambridge-english-readers (Material for different English levels)
Kindle app – Many classic English books for free.
Exercise Books
These are the grammar and vocabulary books that I recommend the most.
Grammar
Essential grammar in use (beginner) – Raymond Murphy
English grammar in use (intermediate) – Raymond Murphy
Advanced grammar in use (advanced) – Martin Hewings
Vocabulary
Oxford Word Skills Intermediate - Ruth Gairns and Stuart Redman
Oxford Word Skills Advanced – Ruth Gairns and Stuart Redman
Oxford Words Skills Idioms and Phrasal Verbs - Intermediate - Ruth Gairns and Stuart Redman
Oxford Word Skills Idioms and Phrasal Verbs - Advanced - Ruth Gairns and Stuart Redman
To get feedback
Ludwig – Correct your sentences (free) https://ludwig.guru/ (this site can also help with paraphrasing)
Grammarly – Correct your sentences (free and paid) https://app.grammarly.com/
Deepl – Translator (free) https://www.deepl.com/translator
Lang-8.com – Get feedback from real people (free)
Italki.com – Find a tutor (paid)
Flashcard Applications
I Do Recall – Easiest to use (free and paid) https://www.idorecall.com/
Anki – More complex but totally free. https://apps.ankiweb.net/
https://fluent-forever.com/chapter2/ (Guide for using Anki 1)
https://fluent-forever.com/gallery/ (Guide for using Anki 2)
Vocabulary Lists
1,000 most frequent words in English https://www.ef.com/wwen/english-resources/english-vocabulary/top-1000-words/
3.000 most frequent words in English https://www.ef.com/wwen/english-resources/english-vocabulary/top-3000-words/