My tips are as follow:
1. Headshots only the front / medium row Ganados.
2. Body shots for moving Ganados.
3. Try headshots female Ganados as they yield 200 points instead of 100 points.
4. Try consecutive shots as many as possible, even if it means firing only body shots, as the Salazar target can compensate for the loss of headshot points.
5. If there is explosive-holding Ganado among others, try to shoot a few those around before firing at the explosive Ganado. The points obtained this way is higher than firing straight at the explosive Ganado as all other Ganados will go down without giving any point.
6. Practice. In my 1st playthrough I sometimes needed as many as 20 retries to memorize the patterns and where to stand.
All my played games have exactly 1000G.
1st 1000G: Batman Arkham Asylum (PC)
1st Xbox360 game: Trusty Bell Chopin no Yume / Eternal Sonata
1st Xbox One game: Child of Light
1st Xbox360 player to obtain Obsessive Compulsive (collect all loots in a single chapter) in Thief on 25/2/2014 at Trueachievements.org