First, a few examples of what an iPhone 4 can take straight out of the camera, no manipulation or post processing done.

Tips and tricks that helped me to get shots like these:
- Pay close attention to your horizons. With a small camera or cell phone it is easy to take a shot tilted from one side to another.
- Become familiar with the focal length of your camera, and pre-visualize good shots
- At night, try using software such as Camera+ to take multi-shot exposures to improve your chances of getting a shot that is blur free
- In the iOS camera app, using the "touch the screen to focus" method really comes in handy. This allows you to set the exposure off of an area of the screen, and also focus where you would like. You almost need to do this in many situations.
Understand that the resolution is not the limiting factor for these cameras. Things like the maximum aperture and sub-par high ISO performance are really where you are going to hit brick walls. This isn't any different from the basic understanding of regular photography, you just have to know that small cameras(sensors) typically have even more issues on a cell phone than a point-and-shoot.
Accept the fact that at least in today's world, the built in LED flash that these units have is nearly pointless. If you find yourself in a situation that REQUIRES it to get the shot, you must understand that the outcome will not be pleasant.
Finally, I absolutely do not consider my iPhone 4 to be the lowest rung on my camera list. I find it to be a joy to carry, pull out of my pocket, and snap shots at anytime or place I wish. I have a high end point and shoot camera(USD $500) that I leave at home, because the iPhone 4 is better, that is right I said BETTER. Better because I have it with me 100% of the time, I don't have to worry about memory cards, storage, battery, or anything of that sort. I can just take pictures, and excellent quality pictures I might add.