Glad to hear that your car finally about to arrive. Mine's been sitting in Spain since 29 July and Virgin are only collecting it tomorrow even though they have had my money for 3 weeks. Doubt I'll see it before 21 September.
There will be a great temptation just to sign the papers so you can drive off, however the most important thing to look for is damage - everything else can be fixed under warranty.
Suggest a very slow walk round to check for panel damage, chips, scrapes etc and in particular scuffs or other damage to the alloy wheels.
It would be better if you can have a friend or colleague with you who (hopefully) won't be so overcome with the dazzle of the paint work and the wondeful new car smell emanating from the interior.
Enjoy the moment.