How to seriuously improve your writing?

I tried IELTS GT 4 times now to get a score of 8 in each area.

The first time i got 7 in writing with no practise some 7 month ago, then 6.5 twice in another test center.
Then 7.5 in writing yet another center. My overall score is 8.5 now. I have lived and worked in English speaking countries for some years, i do read. I practised a lot. The last time it didnt feel like not enough time. Still… not there and not yet ready to give up on it.

I am looking for serious suggestions about what to do as just writing another 50 more essays seem to not get me there.

TOEFL listening lectures: A lecture by a professor of Art