An extensive list of all the prepositions and their uses: https://www.itepexam.com/everything-you-need-to-know-about-prepositions/
when and how to use prepositions: https://dictionary.cambridge.org/grammar/british-grammar/prepositions
Prepositions of place exercises: https://learnenglish.britishcouncil.org/grammar/a1-a2-grammar/prepositions-place
Prepositions of time exercises: https://learnenglish.britishcouncil.org/grammar/a1-a2-grammar/prepositions-of-time-at-in-on
A short explanation of phrasal verbs: https://learnenglish.britishcouncil.org/grammar/b1-b2-grammar/phrasal-verbs
200 phrasal verbs: https://www.englishclub.com/vocabulary/phrasal-verbs-list.php
literally every verb topic explained: https://learnenglish.britishcouncil.org/grammar/english-grammar-reference/verbs
Top 3000 most common words:
https://www.ef.edu/english-resources/english-vocabulary/top-3000-words/
By far the best site for vocabulary practice : https://www.vocabulary.com/
Some games: https://learnenglish.britishcouncil.org/vocabulary/vocabulary-games
C1 practice: https://idiomium.es/examenes/ejercicios-de-examen/nivel-c1-advanced/ejercicios-para-practicar-el-advanced/
IELTS practice tests :
https://takeielts.britishcouncil.org/take-ielts/prepare/free-ielts-english-practice-tests
Information on the IELTS: