10 tips to get Band 7 on IELTS exam

How can I get Band 7 in IELTS exam? People with good English skills are unable to score an IELTS band of 7.  Some of my friends in India told me that they were unable to score band of 7 even though there English. Please tell me some tips to get a band of 7 in the IELTS exam. They were also telling me about the common mistakes which are committed by IELTS candidates. Please tell me the mistakes which are committed by the IELTS candidates so that I do not repeat them again.