contact me pls, i might give you some tips as i have taken 8 times of the ietls ,the first time i got 5 in my speaking ,then 5.5 then 6 ,then 7 then 5.5 then 6.i have a terrible accent ,contact 9462010
剑桥英语有套书叫《英语在用》,里面有两本Cambridge English Collocation/Idiom in Use,分别对应band7评分点里的collocation和idiomatic expression,楼主可以每天看几节,记下话题里能用到的。但是这两个都只有band7才有要求,band6并没有要求使用,所以可能还需对照口语的band descriptor再找找别的原因了。