Hello! First of all, getting max loot radar is the most important thing since Wisps show up on the minimap. You'll need maxed out Loot Radar aura, Thief's Wit and Animal Instinct for your sentinel/companion.
Next up, pick a fast frame of your choosing to run the route quickly. I suggest using a Nova with maxed Power Efficiency and Range so you can skip over lakes and portal directly into Wisp spawn locations.
Time of day also directly impacts the spawn rate of Cetus Wisps. From my testing in this route you get 1-3 Wisps per day and 3-7 Wisps per night and double that with boosters.
To loot the Wisps, simply walk over them. They will run from you in about 5 seconds if you don't loot them immediately, so don't wait around for too long. Try to memorize the Wisp spawn locations so you can use the minimap to spot them and skip looking if there's nothing around.
Here is the full route with all 30 Wisp spawn locations along it. There are more Wisp spawn locations around the ponds and lakes in plains but this is my preferred route:
Direct album link in case imgur breaks direct image again: https://imgur.com/a/VyEluP2
If you prefer the farming route as video instead, here's the route I'm using with Nova, the run takes 2-3 minutes to complete: