I was advised not to fly in the sim type you'll be using prior to your assessment as you will probably be taught to operate it differently to the way your prospective employer wants you to use it, causing you a bit of confusion in an already stressful situation.
Apart from that read, re-read, re-read and read again ALL the info the company sends you prior to your sim assessment and if you can find a cockpit photo/diagram then thats a bonus too.