Not Always Easy
Lilacs are not hard to grow, but you might have difficulty if the weather is not great. If there is not enough sunlight, they might not bloom. They need six hours or so a day. You might also be disappointed if you do not trim back the old stems after they flower. Young stems are needed for the blooms.
Check The Soil
If you give them enough sunlight and trim the old stems as needed, all is well. What could be wrong if you still do not see flowers once spring comes? It might have to do with the soil you use. If you use too much fertilizer, the bush will just grow leaves and a few flowers. Keep an eye on the nitrogen content.