Some strange things come in on the newsfeeds. A recent one was from a Yahoo! question someone had asked about a film they saw where the driving examiner put a cup of coffee on the dashboard and told the candidate they would pass if they didn’t spill any 
during the test.
Apparently, the film (American) was called License to Drive (1988), and you can see the clip on YouTube.
I use the same technique sometimes. Not with an actual drink – I’d just get wet if I did that – but if I have a pupil who tends to drive and brake a bit unevenly (e.g. “like a sack of spanners falling down some stairs” is one description I have used before), I might suggest that they imagine they have a cup of tea sitting on the dashboard and that they should try to avoid sloshing any of it into the saucer as they move off and stop. It’s surprising how often it works.
Mind you, before the benefits have kicked in there are other occasions where if we’d been using a real cup and saucer it would have ended up through the windscreen and 20 feet down the road.