1) Pick a good, disease-resistant variety, suitable for your climate.
2) Plant it in mildly alkaline soil in direct sun. Lack of bloom is generally related to lack of sun.
3) Do not overfeed - annual addition of compost, or a light all-purpose granular fertilizer scratched into the soil around the base every two years is plenty.
4) Every few years prune out the older, thicker stems.
5) For more vigorous bloom, prune off the dead flowers before they go to seed. Do this immediately after blooming - lilacs begin to set next year's flower buds during the summer, and a late pruning may snip these off.