Blu-Tak (brand name) is a putty like adhesive that can be removed and reused. Ref 3A recommends putting a very small dab on each of the four corners of the top plate of the stand, plus a front-to-back strip.
We're talking about pressing down a VERY thin strip of the stuff. Easiest way is to work the blu-tak between your palms or fingers until it's pretty warm and pliable, then "smear" it down hard on the top of the stand. You want the blu-tak to be almost as thin as a layer of paint on the top plate of the stand. Then you press the speaker down on top of the stand.
Tip: if you ever need to remove the speaker from the stand (as I did when I replaced the tweeters) you want to use a hair blow dryer to warm up the blu-tak, then ROTATE the speaker to loosen the adhesive and then lift it off. Lifting straight up on the cold adhesive may pull veneer off the bottom of the speaker!