If I seem to talk a lot about Band 7 it's because it seems to be such a highly sought band. People need 7 for immigration, they need it for some advanced degree programs and even if you don't need a 7, if you need a 6.5 for a university course, for example, your 6.5 will only come if you have at least a couple of 7s or higher.
I have written quite a bit about fluency, coherence & cohesion, and task response, but I haven't really discussed grammar and vocabulary that much. I hope to correct that in this post.
In the public descriptors both for writing & speaking, the descriptors for grammar at band 7 requires some complex grammar. This of course, leads some people to then ask, "Well, what is complex grammar?" Typically, a complex sentence is one that has more than one clause. A clause, as you probably know is a part of a sentence that contains at least a subject and a verb. So, if you can make sentences with more than one clause, that is considered complex grammar. For example,
Florence, which I have been to three times, is one of my favorite cities.
If I could visit any city in the world, I would travel to Florence.
Not only is Florence a beautiful city, but it is also full of historical importance.
I will visit Florence as soon as I finish my studies.
Having been to Florence three times, I believe I know it fairly well.
These are just a few examples that came to my head. Of course, there are many more. An advanced grammar book will give explanations as well as how these structures are made, how to use them and any other rules you may need. If you need any recommendations for a good book of advanced grammar, please email me.