As well as deadheading, you need to ensure that lantana gets at least six hours of sunlight and regular watering. Despite being drought-tolerant plants once established, lantana will benefit from watering in hot or dry spells.
If it looks like flower production is slowing down on your lantana, Janet Loughrey recommends ‘lightly shear back plants and use a light application of fertilizer to stimulate new growth and flower buds’. A balanced fertilizer, such as the PGF balanced feed available at Amazon, can be applied during the growing season to stimulate blooms, this is especially important if your plants are in a container garden.