If you're talking about a Twingo, they're not old enough to have got so bad they'll need mega attention.
I use a microfibre cloth and Autoglym Rubber & Vinyl Care to shine up all the plastics. As above though, a multipurpose cleaner and some elbow grease will do it.
I've seen people brush an entire engine bay then rinse with a hose but I wouldn't have the confidence personally haha