Important note: I am in no way affiliated with Apple Inc
Taking pictures with the iPhone/iPad normally come out all blurry or not focused on the right thing so getting to know your devices camera better does help to make instuctables on the run.
Step 1: Focusing
Step 2: Turning on HDR
HDR stands for high dynamic range. This just means that it automatically takes three photos with different exposures and then composes the three into a single frame with the best highlight, midtone and shadow.
See omnivents comment. He did a really good job at explaining it.
Step 3: Adjusting the Exposures Manually
Step 4: Taking a Picture
When your all ready press the white circle on the right and it will take a picture.
Turning on grid in settings can really help getting the right angle on the picture.
Sometimes HDR will screw up and make your picture look all blurry so don't always use HDR.
Bad lighting = bad photo
If you are going to use digital zoom don't go above 25% zoom.
Bear in mind that I used a iPad Air which has a 5 megapixel camera.
Visit Apple.com to see the differences in they're different iPad/iPhone products cameras.