Learn basic grammar (tenses, sentence structure, sub verb agreement) - Wren and Martin.
Learn and expand your vocabulary - thematic learning ( travel, tech, beauty) and accent improvement & focus on idioms.
Listen continuously english (podcast, book narrating) & copy.
Speaking english daily & engage in regular conversation.
Practice Thinking in English, not your native language! ask questions yourself and answer them in english.
Use software like speech recognition and record your voice, Duolingo.
Set goals & practice daily and review each day.
Make consistency and develop a habit.
Write in British English & read classic novels.
Book's ---
"Practical English Usage" by Michael Swan.
"Word Power Made Easy" by Norman Lewis.
English pronuncing dictionary by Daniel Jones.
The advanced learner's dictionary by A S Hornby.