Lifehacker and Productivity 501 both have recent articles on better strategies for parking when shopping. They are both geared towards the USA, but many of the tips are still relevant (especially as many out of town shopping centres are the equivalent of a US mall).
One thing I have noticed is that there are no tips for avoiding penalties, perhaps they are not as prevalent over there as private parking fines are here in the UK.
I would say the most important thing to remember is to check the rules of the car park, there should be clear signs regardless of whether it is private or council owned. Ensure you are familiar with any restrictions, and what the potential penalties are for breaching any of them.
Also, do not assume that if a ticket machine is broken that you can park for free. As frustrating as it may be, many councils would say that you should not park in a space at all if you are unable to buy a ticket, even if the machine itself is at fault. If there is a sign on the machine saying you can park for free, take a photo with your camera-phone if you can, as you can use it as evidence if you are then issued with a ticket.
While parking charges do only seem to get higher and higher, it’s better to overpay for your stay than to presume you will be finished sooner and then get a ticket for being a few minutes late back to your car. After all, it’s arguably better to pay a few pounds for an extra hour than £25 for a ticket.