Ielts is a basic english test, if you are already comfortable with english then you'll only need to solve 8-10 mocks which you can get for free online, that too only since you need to familiarize yourself with the paper pattern. But if your english is weak, you'll have to improve on it before giving ielts since you'll probably waste your hard earned money. 8.5/8/7.5/7.5 for L/R/W/S will account for the highest score for Canada PR, anything above that wont improve your CRS score. Having said that to get 8.5/8 in L/R you can afford only 2-3 mistakes over 40 questions.