Calm is required
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Agitation is pretty simple. Essentially, you are just moving the liquid around regularly to make sure that the liquid against the film stays fresh.
When instructions say to agitate for 30 seconds, it means that you smoothly and repeatedly turn the tank upside down and then back rightside up. As you do so you twist it a bit so the liquid inside moves up and down and swirls a bit each time.
I like to take about 2 - 3 seconds for each full cycle. So 30 seconds of agitation should result in 10 - 15 cycles. Use the time for each cycle that you are comfortable with, and that you can easily repeat for each roll you develop.
If you decide to agitate every 30 seconds afterwards, then you watch a clock and every time the second hand passes another 30 seconds, you pick up the tank, give it two cycles of inversion in the same smooth and repeatable way. At the end of each cycle, gently rap the bottom of the tank on a towel on your counter-top, and put the tank back down.
If you prefer agitation on 60 second intervals, that works well as well (for reasonably long times). Instead of two inversion cycles every 30 seconds, I would suggest four inversion cycles each 60 seconds - they should take in total about ten seconds.
Agitation should have energy, but not be violent. If you do it to music, something mid-tempo is best - avoid thrash metal or baby lullaby.
It is far easier to show you how to combine inversions and twisting than it is to explain it, but I can suggest an experiment. Take the tank in both hands, with your left hand on the top, and right hand on the bottom. Then use your arms and wrists to invert the tank, ending up with the tank upside down, and your right hand above your left. Watch how the tank naturally twist as it turns upside down - that is the sort of movement that works.