I use a cheap light box with white fabric draped inside set up with large construction lights. They are very yellow so I always set my white balance to tungsten (light bulb symbol) and also colour correct them later as well. I'd recommend day light bulb lamps if you can.
I stand my cards up and try to photograph them head on meaning as straight in front as possible. So my angle is lower for a side fold card than for a top fold one. This prevents distortion of the lines. I love seeing other peoples cards taken at an angle, for some reason that doesn't work for me unless I am photographing the details.
I recommend macro mode on a POS camera or a fast (low max aperture like 1.8 or 2.4) macro lens for a DSLR camera. If you have a DSLR, setting your aperture makes a huge difference in how your picture looks. If you normally shoot in auto, try out aperture priority mode! It lets you control the ISO and aperture but figures out the rest. Low numbers like 1.8, 3.5 etc will give you that tight focus on your focal point with the rest of the card's focus blurring away from that center point. If you set it up at 4+, you will start getting more of the card in focus. All of this depends on how far away you are too as the further back, the more of the card is in focus and vice versa. These are just the settings I've used. I use small numbers for details and larger ones for the whole card and even higher numbers for photographing a 3-D project or a group of cards like 8.0. If you have a card with very dimensional bellies on it, treat it like a 3-D project if you want it all in focus. This principle works with groups of people too. Use higher apertures for larger groups to get everyone in focus.
If you find you photos are blurry, especially at higher aperture numbers, use a mini tripod and self timer to take your pictures. The camera is compensating for low light caused by a small aperture (large numbers reflect a small size opening to let light through) by opening the camera's shutter for longer. Any hand shake is recorded as blur where with a faster shutter, there isn't time for the camera to record that movement because it isn't open long enough.
A too small aperture can also cause blurriness. Look carefully at your photo. Is anything in focus? Even a tiny element? Perhaps the rest is blurry because you have too much of that artistic blurriness (called bokeh) where the focus is tight on one element then fades out around that. Your tight focus area may be smaller than you want or in the wrong place. A damaged lens can also cause this but if some photos are ok but others aren't, that clearly isn't the problem.
If you like to add props to your photos, you can use the principles above to determine where to place them based on whether you want them in focus or not. The further away you place them, to the side or back to front, the more blurry they will appear!