1)NYSC is compulsory.(So you mustn't wait till NYSC is over, you can apply in between the service year, the service year gives you the opportunity to serve your fatherland, and at the same time to prepare for tests like PTDF, GRE and so forth).

2)Result must be 2.1 and above

3)On graduation make sure you get your university transcript ready.

4)At any point have an updated CV.
Have all your documents from WAEC or Primary School Cert, all scanned and kept in a flash or stored in any other form that's handy, so that for whatever application you will have them ready for use.

5)While serving, NYSC, be alert keep contacts with those who share the same dream. Check the PTDF site whenever, they will be advertising. www.ptdf.gov.ng, Normally they advertise for application towards December or early January.

6) You can apply for admission to a UK school, you can get admission easily to the UK and you can apply from early March, April as against September admission, with the hope that you would secure the PTDF scholarship.(Don't wait for PTDF, to secure admission for you as it's wiser to secure it yourself and all they would is to pay for the fees when you have won the award. you can inform PTDF you already have admission to the UK, they would act as your sponsor.)

7)Apply for the exam, and fill the computerized form carefully(Last year scratch cards were sold for the form-N1000). The exam is now electronic.

Study extensively, for the two parts. For general questions (From History, science, education, inventions...), and read for the area you want to specialise in. Make sure you drill yourself mentally with questions on logic, abstract and verbal reasoning. It will boost your IQ. Most aptitude test questions are practiced for, Nobody will know it if not practiced for. So those who don't practice such questions would flopp generally, not matter how good their standing in their academic course work.

9) Pray to God for help, you just can't be too good enough. And find out more information.
Best Wishes