A hedge should be slightly wider at the base than at the top — a gentle ‘A’ shape. That lets light reach the lower leaves, so the hedge stays thick right down to the ground instead of going bare and twiggy. We use a string line for long boundary hedges so the top is level along the whole run.
Flowering shrubs are different. Ixora, bougainvillea, hibiscus and jasmine flower on new growth, so we cut them right after a flush of flowers, never just before.