How should I learn English?

Hello everyone :)
I would like to advise on futher learning. I've been studying English from few years but lately I didn't need it on high level. The result is simply that I've started to make stupid language mistakes. Right now I would like to study English on my own to achieve C2. Unfortunately I feel something like B2. What studying style can you recommend? Reading books in English and watching TV or it would it be better to combine it with some coursebook? Do you think that CPE certificate can provide any profits?

we're waiting for your advice, then

http://www.newsinlevels.com/ moze to 3poziom (gdzies 800filmików)

>>Do you think that CPE certificate can provide any profits?

You can frame it and hang it on the wall in the bathroom. Maybe someday it will serve 'its' purpose.:)

zielonosiwy thank you for your remark, this only shows how much I need to revise English and asked for advice.
emil05 thank you for your link, I really like it :)
I am asking about CPE certificate because some job offers require to have one and I'm considering if it is really that important.
I am thinking if this book http://www.bookcity.pl/repetytorium-gramatyczne-w-zdaniach-do-tlumaczenia-angielski/pid/17518 is good source of language learning. I mean complete learning with grammar and vocabulary at the same time. Have you used it and can say something about it?

No problem!

-Ang. w tłumaczeniach (6cześci= ponad 5000 zdań) + czasowniki frazowe ztego wydawnictwa (bajer)

-"Polyglot ćwiczenia z gramatyki angielskiej 8500 zdań do tłumaczenia" - szybko znajdziesz w sieci - mega opcja ^^

pozdrawiam