Ok, so the 'fishing rod trick' is, in my opinion, quite affective. The general use of the fishing rod trick is to knock back the player as you approach them at a fast pace so that they get knocked back and you get the first hit, if done correctly. You may also use a fishing rod to push the players back if you are on low health. Finally, if you are in a water battle, it is always useful to have your fishing rod in your hot bar if you need to either, knock back the opponent or knock a teammate further towards your opponent. My technique and setup in my hot bar is: 1. Sword, 2. Bow, 3. Fishing Rod etc... I always have my fishing rod out (when not fighting) to ensure i am always ready to use it as someone approaches. Also, to hide my sword so my opponent doesn't know what kind of sword i have. I hover my finger above the number 1 on my keyboard, so that it ensures that i can quickly switch to my sword. Furthermore, I have another finger hovering over the number 3 on my keyboard, just in case I need to switch to my fishing rod again, if i need to knock my opponent back (possibly if i'm on low health).
Tip: (If you don't already know this), After casting your fishing rod out, don't reel it back in, with your scroll wheel or number keys, quickly switch to another item, probably the item next to you, and go back to your fishing rod to ensure your not using up your fishing rod.
Hope this is a good enough guide, if you attempt to do the fishing rod trick, Good Luck!