This is a good source for english writing tips:
Hi there! Welcome back to English Chat. If you remember the 5 questions to ask yourself before learning English, you’ll know that people can have very different purposes in studying a new language. Many of us just want to be able to speak like a native speaker; some want to be able to understand native speakers;
and others actually want to be better at academic writing. Since we
have spent a lot of time on the first two skill sets, today, we are
going to talk about 5 English academic writing tips that will help you
craft a better essay. Let’s get right to it.
I also came across with this post: https://thebestenglishcoach.wordpress.com/2014/04/16/tips-to-improve-your-english-writing-skills/