Bloody Hell! Such interest. Well here goes... First things first - I work with a crab biologist up here and one spot she put me on was brilliant one day and crap a few days later, we tend to get the best results on the neaps (after a new moon) with 2-3m fall in the tide but that varies depending on where you are. Up here in Darwin we can get a 7m change (!!) but down in the bottom of the gulf, around the McArthur River, it's only 2-3m - but generally before and after the neaps work the best. Too big a change, especially here in Darwin (the crabs in the photo came from the Adelaide River) and the pots get washed out of the creeks or stay high and dry for a few hours. We generally fish on a 6-4m change. We crab during the day - easier - and crabs tend to be a little less active at night. We look for creeks that have lots of active holes in the banks. And the more mangroves on the bank, the better. Big contiguous areas of mangroves better then areas where the cover is patchy. Avicennia and Rhizophora mangrove species also the best.
As far as pots go, I use the circular collapsable type but have had good success with the rectangular ones that fold up and join in the middle - don't pay too much for fancy pots - it doesn't really matter what type you use as long as they aren't fiddly - find the rectangular ones the easiest. The bait is the critical thing. The commercial crabbers use horse meat - lots of blood - also used roo meat with good success - and chicken wings are excellent, we put them in "packets" made out of gutter guard plastic mesh "sewn" with fencing clips (little circular clips you close with pliers) - nice and strong although some of the big boys can mangle one in 30 minutes flat. Attach the bait to the bottom of the trap with a cable tie - bait DOWN when you throw the trap in. We tried coating the bait in aniseed oil once but the result was inconclusive - but we use it when we can. Have used Dilly's before but only tend to get once crab per bait as bigger crabs will sit on the bait and push othes away - so when you pull it, you only get one. With the closed pots we get 3-4 to a pull - bit only tend to get one big one at a time - and that leads to another point - we leave the pots in for the first hour and a bit (gives us a chance to snag a barra or two) to get the scent out into the creek, but after that we pull them as often as we can. What usually happens once a big crab goes in, is that it keeps other big crabs out (may have a few smaller ones in before big crab arrives) - so the quicker you can pull him out, the quicker the next big fella arrives. They are very cannibalistic, so big ones will give the smaller ones a bollocking if the bait goes - so don't leave them in for too long. We usually go out with 10 pots (our legal limit for two adults) so that usually means a pot gets pulled every 30-40 minutes after the first soak.
Size limits are 14cm carapace width for ladies (and yes we can kep non-berried jennies) and 13 for the boys but they must be full (ie not just moulted). The photo I sent didn't include two that had scuttled under the car behind us while we weren't looking - not sure of our limit (my "rule book" is in my tackle box) but I think it's 10 per adult, max 35 per boat) and that day we caught at least 20 other females that were legal but empty so threw them back. Which brings me to a final bit of info - they breed (up here at least) just before the wet and they have to moult to breed. jennies with eggs go offshore to spawn - way offshore - so forget any decent catches between November and February - all you'll get is sad old males (and very few of those) and juveniles that mostly hide in their holes.
Here's a before and after - just so you can tell the difference between full and empty crabs. Good luck boys.