I'm not a photography expert by any means, but I have learned a couple of things along the way
Tip #1 The Rule of Thirds
Have you ever seen grid lines on your smartphone or camera? They divide your photo into thirds. Place your subject along the corners where these lines intersect. You'll get more of the scenery, and the photo will draw your viewer into it. Unless your subject takes up the entire frame, you shouldn't place your subject in the center.
Tip #2 Cropping
Sometimes you need to determine what's the focus or purpose of your photograph, and what's a distraction from it.
Cropping (or cutting away/removing a portion) helps your viewer focus on the subject, without the distractions. After all, the subject is why you took the photo in the first place, right? You can also get a more detailed (like zooming in) photo of your subject when you crop away all of those distracting pixels.
I sometimes struggle myself with what's the subject and what's a distraction. If the background isn't particularly scenic, I wouldn't really care to display it to the world. Cropping it out just gets rid of the "noise."
Tip #3 Depth of Field
To keep your photograph from looking "flat," choose a scene with something in the foreground, middle, and background before taking a picture. What you decide to focus on is up to you, and depends on what you determine your subject to be.
Choosing a scene with more than a single plain of focus gives your photograph depth or distance. Instead of a simple 6 feet of depth (shallow), you can achieve up to 10 miles of depth. That's pretty deep! But the distance doesn't have to be great, you just need a front, middle, and back.
Tip #4 Diagonals
Diagonals and s-curves guide the eyes of the viewer. They're great for perspective and depth, and can divide your photograph into foreground and background.
It should be subtle. You shouldn't notice it. But your eyes should be naturally drawn down that diagonal.
Tip #5 Framing Your Photograph
Finding a natural frame or border for one or more sides of your photograph can help draw your viewers eyes to the center or subject.
The frame doesn't (and often shouldn't) encircle your entire photograph. Along one side, or even in a corner is often sufficient. Framing your photo also helps provide depth of field (see previous tips).
Tip #6 Using a Flash to Defeat Shadows
I don't know why so many people freak out when I tell them they need to use flash in broad daylight. Flash is the shadow defeater!
Broad daylight, or a backlit scene, can create strong shadows or silhouettes. Use a flash when shadow is covering your subject. Since my habibi is perpetually wearing a cap, I have to use a flash to show his face.
Tip #7 Seek Unusual Angles and Perspectives
If you're photographing the same old thing that everyone's already seen, try photographing it from a new or unusual angle. It can also provide depth and keep the photo from becoming flat (see previous tips).
It'll give your photo a fresh new perspective. And who knows? You could start a new trend! Of course, that would mean you'd then have to find another new and unique perspective.
Tip #8 Ensure Your Subject Can be Easily Seen and Recognized
If you're taking a photo of your significant other with the Eiffel Tower, ensure your significant other is close to the camera in the foreground. The tower, a globally recognizable object, can easily be determined from the background.
Having your subject stand 100 meters away next to the Eiffel Tower not only flattens your photograph (see Depth of Field above), but makes the individual indiscernible from any other human subject. An exception to this would be a desire to show scale. But even then, try to ensure your photograph doesn't turn out flat.