First see Higher Study Prep’s youtube videos. Higher Study Prep’s free videos are available in youtube.
Practice writing at least one letter and one essay everyday.
I started from cambridge 13 to 1 in reverse order. Do read answers at last given in that pdf because when u read given answers and reasons mentioned for scoring, you can judge mistakes in your essay.
I also had barrons test book, which can be solved and compared answers. It will give you idea and thought process required and expected for writing.
Try to write complex as well as compound sentences with proper punctuations in your writing and do ensure everything required in essay question is covered in your answer.
For speaking, try to speak loudly on essay topics by yourself so that you can know the way you speak and compare them with videos on YouTube.