In answer to the first post, visiting your local library can be really helpful regarding the history and locations of older areas around your neighbourhood. Once you get a good idea on which areas were occupied back into the 1800's or early 1900's, pre-decimals can pretty much occur anywhere, and sometimes in the least expected locations.
The next step is to simply test an area to see what coins pop up (ie. Park), there is no real secret formula to success, just persistence and patience will usually reward you with some older coins.
Many predecimals may not be obvious targets like shallow modern coinage, sometimes just faint deeper high tones amongst the louder modern targets in the ground. Take your time to investigate the deeper targets, swing your coil too fast and you may simply overlook them.
You should be looking for repeatable high tones with reasonably steady ID numbers, most irregularly shaped junk and canslaw with have ID numbers jumping all over the place, whereas coins should remain steady. Some iron targets that give off high tones can be identified by wildly fluctuating ID numbers, jumping sometimes from very low numbers right up into the high 90's.
Don't get too stuck on trying to identify a possible coin target using ID numbers, if it is deep, the less likely that the numbers will be accurate, hence you should revert to using tones as your best guide on whether to dig or not.
Also use your pinpoint function to size up a coin target, no point digging a high tone (high conductor target) if it pinpoints 30cm wide, as it will more likely be a large target at depth (ie aluminium can). Coin targets should only pinpoint as small targets when scanning the ground, unless you are lucky enough to come across a spill of coins.
Also avoid detecting any obvious Heritage sites or around older buildings that might be protected, unless you have prior permission, preferably in writing.