Indeed, use fairy liquid and warm water to wash your car, rinse off then use something like P21S paint cleanser which will remove wax and prep the paint for whatever product you wish - I suggest reading the Polished Bliss guides on paint care:
http://www.polishedbliss.co.uk/acatalog/guides.html
http://www.polishedbliss.co.uk/acatalog/guides.html