I was trying to think of a quick tip that might help beginner photographers improve but that didn't take an hour to read.
If your camera has live view (the digital screen) then you can use it to make sure your images are really in focus. On Canon cameras, you can zoom in 10x and move the focus point to make sure the thing you want sharp is really in focus. This does take time so is best for night shots, landscapes or still life macros etc where the subject isn't going anywhere and your camera is on a tripod, but actually can still work if you have steady hands and stabilisation. However, in one YouTube video a pro photographer recommended to use live view to focus then turn it off before taking the shot... I totally disagree with that and here's why-the live view image is coming straight from the sensor. Turning live view off and looking through the view finder can cause the focus to shift when you press the shutter button. Unless you have made sure your camera and lenses are completely in tune using custom micro focus adjustment then you risk getting a less focused image than with live view. But that's for another blog post.