First, learn which formats are being used by your test center. There are no major differences between centers but still worth knowing beforehand. Also, some centers offer courses (online or on-site) before the test where they give some tips & tricks which might be useful but in the end, as Airgus wrote above, it all comes to practicing. Some personal trick for the speaking module (e.g general questions, picture description, etc) is to record your answers, then listen. Also, there are some quality youtube videos worth watching, just search "ICAO level".