I have been to Sassafras Gully a couple times this year to some success. Haven't found any snakes there, though have found a few species of gecko and dragons. There are a few trails just near Glenbrook that I've been through, Tunnel Gully Reserve ( was hard to find the entrance), Bluff Reserve and Jellybean pool. Jellybean pool was the only place I found anything in that area, found a Bandy-Bandy, a few gecko species and frog species. All trips were at twilight/night.
I plan to head back to Jellybean pool in a months time to spend a whole day/night out there.
I've also heard that near the Penrith Lakes National Park can be good.