Answer: Your Russian lilac, Syringa vulgaris 'Krasavitsa Moskvy', has exceptionally fragrant flowers so I know what you're describing. I'd want to encourage more blossoms, too! Lilacs should be pruned immediately after flowering because they take all summer to develop flower buds for next spring's floral display. You don't have to prune your lilac if it is still small, but you should snap off the spent flowers as they fade. If you look closely you will see two tiny buds on opposite sides of the stem just below the base of the spent flower. These buds are the developing flower buds for next year's flowers. Try not to damage them when you snap off the flowers.
If you need to prune that particular branch back because it is too long or unruly, you can do so and new flower buds will form later in the summer. Most gardeners reduce the size of their lilac bushes by about one-third every year. They get fewer blossoms but they manage to keep their shrubs in control. I tend to reduce the length of some of the stems each year, alternating which ones I prune so I'm always assured of a floral display the following year. As you get to know your lilac, you'll begin to understand how it flowers and you can prune either for lots of flowers or for compactness and controlled growth.
Hope this answers all your questions!
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