When lilacs are in bloom you will know because they smell absolutely wonderful and provide a show of excellent colors! Most lilacs only bloom for 3 weeks in the spring, but there are exceptions...like the 'Bloomerang' and 'Josee' cultivars. They are the only re-bloomers that do well in our climate. Lilacs can withstand shade and will actually be perfectly fine, but they will not produced nearly as many blooms if they are shaded. They like at least 6-8 hours of full sun each day. The more sun they can get the stronger scent and more blooms they will have!
The best time to prune lilacs is just after they are done flowering because they will start producing new buds that same summer. If you prune a lilac in the fall you are most likely eliminating next season's flowers.
Lilacs are one of many species of plants that are more susceptible to powdery mildew than others. 'Bloomerang' cultivar is an great option for powdery mildew and deer resistant.