The primary difference between the old and new flight plan form is the use of additional alphanumeric codes in certain sections of the flight plan. While most of you are probably familiar with filing /G for the equipment suffix, the new form will require more information to be entered in this field. The expanded number of flight plan codes specifies not only what type of equipment is installed, but also the capabilities of that equipment. The changes are designed to gather more information about how your aircraft is equipped, and to offer the best procedures available, based on your capabilities.
- changes to indications in Items 10 and 18 (including the use of digits) describing the precise NAV/COM/SUR capabilities of the flight
- the ability to file a FPL up to 5 days (120 hours) before the flight, using the Date of Flight (DOF/) in Item 18
- addition of new Item 18 indicators and changes to the contents of several existing indicators.
- a change to the description of a significant point which may now be described by range and bearing
OF course I can't give you all the most precise explanation about the changes done by ICAO, but you can have a big help from Eurocontrol on this link:
Have a look before you prepare your Flight Plan, especially for IFR flight, if not ask your instructor or your local Aero Club.