PREPARE TO GET 8 BAND. UNFORTUNATELY THERES NO SHORTCUT.
To most of people, hardest is reading. So read academic english, especially reports and journals about different topics. Speed reading with understanding is required.
SPEAK English as much as you can, with friends and family. Reading english loud will definitely improve your accent and make the process of motor neurons faster, and you brain will start processing words quickly. Think about any incident happened in past, write that down in english and read that loud. speaking loud improve fluency.
Download english sub titles of a movie, read them through, find difficult words, find meanings, try to remember meanings, read sub titles again, then watch the movie. Your brain would pick words quickly as it already new meanings?
Try to avoid grammatical mistakes and write fast. One section could be writing your analysis about a graph or chart, Important bit is dont miss any information give in the chart while writing it into report.