It really depends on a number of factors, one of which is your understanding of the test and requirements of the band scores. If your English is suitable for the band score you are aiming for, you will only need to focus on exam skills to make sure you reach your potential. The skills will help you understand how to approach questions and what the examiner is looking for in your writing and speaking. Once you feel comfortable with all that, you will have a clear idea of how long you want to practice before your test. Whatever you decide, make sure you are frequently getting the band score you want in practice tests.
All the best
Whenever possible, use strong subjects and active constructions, rather than weak verbal nouns or abstractions and weak passive or linking verbs: instead of "Petruchio's denial of Kate of her basic necessities would seem cruel and harsh...," try "By denying Kate the basic necessities of life, Petruchio appears cruel and harsh--but he says that he is just putting on an act." Don't forget that words and even phrases can serve as strong sentence subjects: "Petruchio's 'I'll buckler thee against a million' injects an unexpectedly chivalric note, especially since it follows hard on the heels of his seemingly un-gentlemanly behavior." And remember--use regular quotation marks unless you're quoting material that contains a quotation itself.