Hello! Of course, I don't mean learning English from scratch. But I would like to have a higher level and speak more fluently. Any tips?

In my opinion, you just need to find an experienced tutor, of which there are many online now, and also have more speaking practice. This is more than enough.

If we talk about self-education, which is now also quite possible and effective, I can recommend the Promova platform and the learning materials that it provides. Here https://promova.com/english-grammar/adverb-clauses-in-english I learned more about a grammatical rule that I couldn't understand for a long time. The information is very clear, structured and easy to learn.

run 3 You should not be afraid to give a website a try if you come across one that seems to be worthy of your time. There is a good chance that you will get reimbursed for the efforts that you put forth, so you should not be disheartened by the prospect of doing so.