There numerous differences between Western and Eastern or Vedic Astrology. Too many to go into depth here.
One of the main differences is in the calculations that the two systems use. Jyotish uses what is called the Sidereal zodiac, which is based on fixed observable constellations that we can see. Western Astrology uses tropical zodiac, which is based on the relative and changeable position of the Sun.
In Jyotish we look at clients Lunar Division of the Zodiac, Nakshattras, as suppose to Solar division of the zodiac that Western Astrology uses. The lunar division is a lot more precise as Moon travels 13 degrees and 20 min a day through the Sky, as suppose to 1 degree for the Sun. There are 27 Lunar divisions and 12 Solar ones. The position of the Moon at the moment of person’s birth also sets for a system of planetary cycles and sub-cycles, Dasa -Bhukti system, one of many tools helping us accurately predict events in person’s life.