In photography, there are several ideas behind the creation of a strong composition. The first of these is called the rule of thirds, which refers to breaking your frame into three parts either horizontally or vertically and weighting the composition along one side or the other and not fully centering every image. The second is called the golden ratio or golden spiral, putting more focus in the corners of the image and spiraling outward. Both are extremely successful but should be considered while photographing and not after the fact.
Another major compositional technique is called leading lines—this refers to perspective or actual lines in the image leading to the part of the image you want your viewer to notice. It is essentially highlighting the important subject of your photograph.
Last is framing--use natural framing (windows, doors, etc.) or make sure to compose your image how you want it to look while taking the photo and not later in post-production. Cropping is an option but it is always better to frame the image with intent.
There are several editing apps available for free download, but the editing app on your phone will offer a lot of easy options. First, crop out any extraneous information that isn't important if you didn't do this while framing the photograph. Second, don't use filters. If you want your photo essay to appear as professional as possible you need all of the images to be cohesive. Adding different filters to several different images will create a choppy, not to mention amateur, visual. On this same idea, obviously do not use snapchat or instagram story filters.
How to take better photos with your iPhone.
Here are some quick tips to maximize your photo taking success.
1. First things first...don't zoom! This adds a lot of digital noise to your image and instantly decreases quality. If you need to get closer I would crop something out in post-production rather than zoom in during the photo taking process. But better yet, physically get closer to your subject.
2. Don't use flash, if you need more light use a friend's phone to add "off-camera" lighting.
3. Try using the grid option on your camera to help compose your images (hello rule of thirds!).
4. Change your exposure. While taking a photo, click on the screen to focus and expose for your subject, when the box with the sun pops up slide your finger up or down to brighten or darken your image.
Below is a quick video with 5 tips for making better iPhone photos.