When taking a photo it is very important that the colour of your subject does not blend into the background. Try to use contrasting colours so as to attract viewers and remember that different colours can make viewers feel different things (blue can make someone feel sad).
If a camera is not focused on the subject(s), the end product can appear blurry, and what could have been a great photo could be ruined. Focus on your subject, rather than focusing on everything. Use the manual focus if there is a specific item that needs to be focused on, because the automatic focus will just focus on everything in the viewer.
The rule of thirds is something every photographer should live by. Occasionally it's nice to have the subject dead center, but most of the time it is good to have the subject on one of the intersections of the four lines on your camera screen.
Horizons are everywhere you look, and a popular thing to photograph, but if the photo is not taken properly it will not look good. Positioning a horizon in the very middle of a photo can make it look like two separate pictures, so put the horizon just below or above the centre of the photo.
Sometimes, the zoom on a camera isn't enough to make a photo look good. It's times like these that it's good to get closer to the subject because often, a close-up picture can look better than a further back point of view.