Hi Pilot16,
Congratulations on passing your PPL! Great feeling, eh?
You might as well start studying for your ATPL's as it'll a good few months for the CAA to get there act together and get your nice new shiney brown folder with "JAR-FCL Private Pilots Licence" written upon it sent out to you. They'll cash your cheque within a day or two though. <laughs>
Anyway when you do get your PPL in your hands then for hour building I wouldn't just burn holes in the sky.
Use it fo practice VFR navigation. For that is what the JAA CPL test involves (its basically like a JAA PPL Skills Test but to stricter standards).
Practice holding headings precisely as well as height. Get trimming the aircraft as second nature (you'll know what trimming an aircraft means when doing your IR!). Have a checkout (a think you need an endorsement nowadays) on an complex type as having experience in say an Arrow will do wonders for when it comes to your CPL training (the test is on a complex aeroplane).
Do an aerobatics course to make you feel a lot more confident in the airframe.
Get some tailwheel time...
Do some flying abroad.
Take friends / family flying - for lunch to Le Touquet / Jersey maybe?
Above all just enjoy your flying!
Best wishes,
Charlie Zulu