I love using Lily Grass for bouquets. It is a little stiffer than bear grass and pushes easily into the florist foam.
It's long broad blades are beautiful as corsage and boutonniere accents as well.
I make a clean cut on one end (using scissors is ok on this type of greenery) and pushing it deep into the foam of the bouquet holder.
I cut the other end in the same manner (diagonal cut) and insert into the outer part of the bouquet holder, thus making a loop over the greened bouquet.
I do this several times, both in the upper and lower part of the bouquet, giving an illusion of a armature of grass around the other greens.
Push some grass tips (non looped) in the lower right, coming out next to the bottom loops.