I have done the apt test at PTC in July and am starting the Flybe mentored pilot scheme in October. I already hold a PPL. The tests are striaght forward, and there is nothing you can really practice, you can either do them or you can't! Go on to google and put pilot apt in and you will see two or three web sites that offer similar tests to what you will be doing.
www.pilotaptitude.com This is a good site, and just to put my two penneth in I believe that testing is a good way of seeing weather you have the ability to do the job before you hand over a serious wod of cash.
Anyway hope it helps and good luck, and i might see you there. 