Design rules for 3d printing

Hi,

I am trying to compile a list of design rules that could/should be followed in order to successfully model and manufacture a part by 3d printing. As we are aware, 3d printing has given us more freedom in the design state, however, it has its limits, for example there has to be a minimum wall thickness , or overhangs should have support structures, etc. I believe some rules will apply to certain technologies, materials or features.

Anyway, what rules do you think we should follow when designing for 3d printing?

Looking forward to your replies.

Granted, this is probably a question best answered by people who actually own a 3D printer rather then me... But I'll get the low hanging fruit first. :p

For FFF, consider your overhang. If you have features of your part that are at less than a 45% angle from the build surface that are not 'bridges' to another feature of the part, you'll need supports for that feature to keep it from warping, sagging or even outright failing.
Know your bridging distance. Sometimes you'll see a prospective printer doing a "bridging torture test" showing filament being pulled through thin air between two features at the ends. While a printer can theoretically do that, there is a high probability of failure, and even success has a lot of warping involved.
for materials with lots of shrink (most popularly ABS) make sure the base of your design is very thick and robust to keep it from curling up off the plate and warping the whole part. I've seen some folks print tabs extending out from the corners of the print to give a wider footprint on the build plate and help the part's corners remain stuck down to fight against warping.
Less obviously, mind the grain of the print, for circular bearing surfaces for instance, a circular hole or boss that is perpendicular to the build surface will be smooth, while one oblique or parallel with the build surface will have a grain that can cause it to stick while turning.

The rules for SLA and SLS are much different from these, especially when dealing with overhang and bridging. (one big advantage of SLS, you never need to design supports.)