My agitation method was learned when I worked in a custom B&W lab. I processed all roll film in tall stainless steel reel tanks (4 rolls of 120, or 8 rolls of 35mm per tank) by hand. Usually in D-76 1:1.
Start with a water pre-soak for at least 30 seconds. This is a good practice because it takes longer to fill the larger tank through the cap.
Once the developer is poured into the tank, give it a few good wraps on the counter to dislodge any air bubbles. Immediately start your tank inversions. The agitation is fairly vigorous. Initial agitation is for 30 seconds. The inversion rate is about one complete inversion (over and back) per second.
Subsequent agitation is 5 - 7 seconds every 60 seconds. Four inversions during the 5 - 7 second agitation period, with a bit of a drop at the end of the inversion. I also gave the tank a half twist during each inversion. Alternate the twist clockwise, then counterclockwise, on each inversion. Wrap the tank a couple of times on the counter after each cycle to dislodge any air bubbles.
Twenty seconds before the development time was up I would start draining the developer out of the tank.
I could process 4 tanks at the same time by having each tank's agitation cycle start at 15 second intervals (00, 15 sec, 30 sec, and 45 sec). I would stagger my start times so that I had 30 seconds between the ending time of each tank.
This process gave us wonderful and evenly processed negatives, even though the agitations were more vigorous than I had been used to.
Whatever method you decide to use, keep in mind that consistency is the key. Use the same method every time and remember that your agitation rate affects contrast.
Your negatives will show you if your technique is working. Too vigorous of agitation will give you streaks from the reels, and too little agitation will give you mottling.
As Nworth stated above: agitation is a very personal thing. Good luck.