Hello,
Without a doubt the preparation and practical exam for the intial CFI is by far the toughest thing that I've ever done. Tougher than the military, college and everything else I've experienced in 43 years. The flying is really the easy part, it's the bloody oral and making sure that all your "ducks are in a row" i.e., paperwork, aircraft maintenance records, etc...Just seemed like so many pitfalls to trap you somehow.
Archer-
Don't sweat the small stuff on the VFR flight planning. Work together with your instructor to develop a logical "step-by-step" method that you can use over and over again. For instance:
1. What is my mission? destination?
2. Weather
3. Weight and balance
4. Performance considerations
Then make some decisions:
1. Do I have adequate fuel plus required reserves to safely conduct the flight? If not you might have to plan for an extra fuel stop, or reduce your payload in order to upload more fuel.
Once you've looked at the "big picture" you can then move onto preparing your charts and NAV log. The NAV log is a tool for you to use in measuring the actual track, GS and winds during the flight and to adjust your heading and update your ETA and fuel burn. This is very critical if you are planning a flight on the edge of your airplanes range for the fuel load. Unforecasted winds may require you to make a fuel stop. The MAIN purpose of the NAV log is to remind you to keep a good eye on your fuel as the flight progresses.
Lastly, use every available means to back-up your pilotage naviagation. If you have the tools use them, however, don't get into the habit of using the GPS exclusively. It's a great tool, but EVERY pilot needs to know how to navigate by pilotage and dead reckoning, not the "black box". Mariners and pilots have used dead reckoning since the early days of exploration and the fundamental equation of rate X time=distance still holds true today.
Best of luck,
ex-Navy rotorhead
P.S. IFR is cake compared to VFR nav!