The Shulchan Aruch in 651:9 writes that shaking the lulav involves moving the lulav from you and shake three times and then back to you and again three small wavings.
The Rama writes that one moves his arms back and forth 3 times and the shaking is while doing those three back and forths. It seems they both hold that the leaves should rustle a little.
Regarding how strong the waving should be the Nitei Gavreil perek 54:13,14 writes that one should not shake forcefully only enough for the leaves to rustle.Another opnion holds that one should shake the lulav with forcefulness.
Whatever it maybe any type of waving is good (Shulchan Aruch sief 11.)