It's helpful to begin with the idea that one of the important steps of writing development is that you need to constantly be learning:
You need to learn in particular about English. You should be studying grammar and vocabulary on a daily basis. Grammar study is helpful, not only to avoid mistakes or to edit mistakes after you've made them, but also to develop your grammatical range. In fact, that's one thing they are judging your writing on, on the IELTS exam. Grammatical range is your ability to use a variety of structures as you write.
You need to be reading on a daily basis as well. It's most helpful to read certain kinds of materials. But reading, in general, on a daily basis will help your writing. Because it's good for vocabulary studying and you will notice grammar structure in what you read that maybe you are not familiar with. Reading also exposes patterns in writing, such as, how authors organize information, how they use examples, how they present ideas. This is also helpful information that helps you to learn.
Are you writing IELTS practice questions? Are you just writing an email to a friend?
You wanna take what you've learned and apply it to your writing. Find newspaper articles, find magazines, find web content that fits this kind of model where you can read it and get something out of it in general. But then it's gonna push you to learn and study new things.
You're going to really study any kind of grammatical structures or try to ask, find answers to grammatical questions you have about what you've read. As you study, using only English to English dictionaries is the optimal way. If you're translating to your native language, that's not as helpful as if you're able to define new words and you find synonyms in English as you study.
Finally, then, after you've read something, a newspaper article, a magazine article, whatever it is that you've chosen, put it away and then try to write a summary. This is a great exercise for trying to remember a new vocabulary, trying to put structures to use. It's also a good activity for just examining how much you've understood from reading and then putting that language into writing.
The other tips and tricks are provided later.