Any time you change your heading (or plan to change your heading), write the time (2 digits, minutes only), followed by the heading (3 digits).
Example: say you are flying heading 090 and you begin the leg at 1410. At 1415 (5 minutes into the leg) you realise you are off track, to the left of your desired track.
There are many ways of getting back on track, and no doubt your instructor has taught you a method. By way of example, I'll assume you are 5 degrees off track, and you are using the "double track error" method of correcting - although the shorthand will work with whatever other method of correcting you might have been taught.
Using the double track error method, you should turn right by double the amount you are off track. That would mean turning 10 degrees right, onto a new heading of 100. Hold this heading for however long you were flying the previous incorrect heading for (5 minutes in this case) then remove half of the previous correction - in other words, in a further 5 minutes, turn onto heading 095.
So my plog would read:
15-100 (that's the time and new heading that I've just turned to)
20-095 (that's a reminder to myself of the next heading I'm going to fly, and when)
FFF
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