"But in order that the liturgy may be able to produce its full effects it is necessary that the faithful come to it with proper dispositions, that their minds be attuned to their voices, and that they cooperate with the heavenly grace lest they receive it in vain." (SC.11)And again:
"Mother Church earnestly desires that all the faithful should be led to that full, conscious, and active participation in liturgical celebrations which is demanded by the very nature of the liturgy, ..." (SC.14)I read this as a call to a "Marian" participation in the mass: deeply interior, attentive, sensitive, receptive, continuous and unbroken. (Think of a pupil fully dilated.) I do not read this as a call for the laity to "do more things", but to make a total self donation to God through the celebration---to really pray without ceasing, with one's whole person, for the duration of the Mass. (If we can't do it under ideal conditions, what are the chances we'll succeed at prayer when things get tough?)
I've already received a great deal of helpful input from helpful persons. Perhaps you have your own insights to share?