Basically just do all the usual secondhand car checks. Eg: Like checking for rust in common areas; exhaust/rear wheel arch wells etc. Make sure all the electrics work; lights, hood, windows etc.
Guide for new members/potential owners here: http://www.350z-uk.com/topic/22880-guide-for-new-memberspotential-buyers/
Buyers guide: http://www.350z-uk.com/topic/77426-buyers-guide/
350Z service schedule (good to take a long when viewing Zeds so you know whether it's been serviced as per the schedule): http://www.350z-uk.com/topic/31110-service-schedule-for-a-350z/
Sure some others will have more tips for you. Good luck with the Zed viewing and welcome aboard.