i personally don't keep one but if i did i would log every fish caught and on what or what you had the hits on, what others were catching them on, the date and the exact location, also the river conditions.
ex.
1.09-18-01
2.10lb silver
3.6" float 6' leader pink 1/4 once jig tipped with shrimp. had 2 hits fishing a #4 black vibrax. some guy caught a jack on a small pink corkie and eggs drift fishing.
4.under the bridge below the hatchery on the whatever river at the bend casting tword the rocks
5.clear water about 10' down on the sand bar from the bushes
tyler