I have a beautiful Japanese Lilac tree in my yard. I planted it the year after moving into my house, and for the first three years, it did not produce any blooms. I read, somewhere, that brewed coffee grounds sprinkled around the base of the tree would encourage growth. Since there is no shortage of brewed coffee grounds in my house and knowing that coffee helps me to get going, I happily sprinkled my recycled grounds around the tree....to my amazement, there were blooms the next year, and more each year thereafter. I have a happy, albeit caffeinated, tree. To go with that coffee, a spray of 1/2 cup milk mixed with a gallon of water will help defend against disease and pests. Also, lilacs don't like wet roots, so plant your tree on a slightly elevated or slopey area.
As with any stick-stemmed blossom, such as a lilac or hydrangea, before arranging them in a bouquet, pulverize the tip of the stem, about two inches from the cut, so that the stem can absorb the water more efficiently, otherwise, you will have a quickly wilting bouquet. Fresh flowers from your garden make a beautiful centerpiece for a dinner table, either casual or formal. Here, I mixed a few of my lilac blooms with store-bought hyacinths and hydrangeas in a McCoy vase....so pretty, and fragrant!