In this stage we will start to properly study for the exam, So the first step is to get the C1 level, and the second to improve it.

COMPLETE ADVANCED  SB + WB

I have to say that all the preparation books for the Advanced are quite similar but I liked this specially. It continues giving some interesting vocabulary, phrasal verbs and grammar.

I also started to use another book only for grammar which is called Oxford English Grammar Course Advanced and is suitable for both C1 and C2 levels, I didn't finish the book but I will use it again for the Proficiency exam.

And last but not least important (in fact, the most important one!) phase. Sadly, the Advanced Exams is more about repeating exercises similar to the ones in the exam than really studying English (However, you will need a good English level to pass the exam)

I used a wide range of different books that include mock exams with key and audio.

The books are Cambridge English : Advanced exams (it is a collection of books) , Advanced Trainer (Cambridge), Cambridge English Advanced Practice Test Plus 2 (Longman) 

*Please note that since 2015 the Advanced exam format has slightly changed, all the books that are listed here include this new format*

While I was doing my practice test I wanted to know how would I score in a real Advanced test, so I found a document that correlates the score you get in the practice test to the one you should get on your certificate (Eg,  If you get 32 marks in the reading part of the mock exam it equals to the C1 level - good job! ) . The document can be found here.

For me, preparing for the exam on your own has various pros: one of them may be the economic one as it is cheaper than preparing it in a course. The other, is the flexibility of this method, as you can strengthen your weaknesses and study whenever you can (and whenever you want) BUT PLEASE NOTE THAT IS IMPORTANT TO HAVE A STUDY ROUTINE

The main downside (apart from the necessity of having a routine, which is a big one) is preparing the writing and speaking parts. Although there are resources (as the one I've said before to correct your writings) except you pay a private tutor, will always be bots so the corrections will not be very accurate. Another problem of this, is the grading as it is so difficult to grade your own exercises  (being objective) even with the guidelines provided by Cambridge.

So, my tips for these two parts are :

1. Use forums to improve your writing and share opinions with other people
2. Record yourself 
3. If you wish to, use resources as italki  when you can have skype conversations with teachers (I didn't use it but I've heard good opinions about it) there are also, free apps as Speaky (which I've used and it's free) but I didn't particularly like it, as 90% of the chats (which are normally by text) are useless and will not help to improve your English in advanced stages. (Though I recommend it if your starting in a language)
4. Make a strategy. As I was preparing the exam I finally realized that it would be really difficult to pass the Speaking and Writing part with a good score (or pass them at all) So, I focus my preparation on the other three parts of the exam to get the maximum score I could because in this exam it is not compulsory to achieve the C1 level in all the parts but the average of all parts should be C1. So, I scored in Use of English the equivalent to C2 but in Writing my level was B2 and the average is C1.
5. Take the Computer-based exam. If it's available, I highly recommend you to sit a Computer-based exam. Why? In my case, I prefer writing on a computer than on a piece of paper because it's quicker and cleaner. But, there's also another advantage, the listening part, I heard lots of people complaining that in the "traditional" way it is really difficult to properly hear the audio as it is played in a speaker for all the class, whereas in the computer-based you can have your earphones, each audio is played individually and volume is adjustable.

IT'S ALL ABOUT TIMING...

*All the books I used can be easily found on the Internet.