I got a parking ticket in Pasadena & decided to fight it using my law enforcement experience... but how I won is common sense.
When the 'officer' arrives to court for some citations like speeding or metered parking, s/he must bring some evidence of calibration / service for the specific meter you were parked at.
I argued the parking meter cheated me by 5 min, the parking attendant brought the service records for a different meter and I won.
...these service records are great to expose how inaccurate some meters are as well, even if s/hed brought the right one I could still win.
For speeding tickets it should say either "paced" or "radar" on the citation.
Paced means the officer followed you and used his speed-o to determine your speed. Police cars go through AAA sponsored calibration, and they are almost never accurate. The officer must produce this calibration in court, if he says you were 10MPH over but his calibration is off +/- 5, you have a great chance of winning, or paying a hell of a lot less. If he forgets or brings calibration for a unit he was not driving that day... you win.
A few times I showed up to court before noticing the unit I had been driving was off by up to 15 MPH, I let the court clerk know and she dismissed the charges..
Police cars take a beating, units get wrecked, break and are otherwise abused almost 24/7.. the speed-o-meters are no exception and sometimes after a crash cars dont get calibrated right away, or at all.
Radar means, duh, radar.. these too must be calibrated, and they are almost always off by a few MPH. I used to calibrate my radar using a tuning fork, if I didn't... the Coke machine clocked in at 40-43MPH. Make the officer prove his radar isn't screwed.
You can also have your car calibrated, I think AAA will do it, if its way off you can turn a speeding ticket, moving violation, into a "fix it" or equipment violation; think insurance costs.
For parking tickets, look up the violation and read it. If the law says a sign must be posted every 100 feet and the signs are gone, unreadable or blocked by tree growth... you win. If the paint on the curb / sign is faded or otherwise not clear, you can win.
You'll need clear pictures to make your case.
Some state laws even define how big the font on a sign must be, most private parties buy signs at hardware stores that may, or may not be legal in your state.... a legal no parking sign in Colorado might not be in Cali
The "system" is using the letter of the law against you, its only fair you can stick the same pissant regulations up their brown eye.
Last but vital, the 1st question the traffic judge usually asks the officer is what you said when the officer contacted you... the officers copy of the ticket has space where s/he can leave notes you will never see, I used to jot down what the drivers said here... if the officer says you admitted to speeding, ask to see the officers copy... it might just say you were an A hole or jerk with nothing about speeding.