Always try to think about thirds and, if you have a grid in your view finder, use it until you get more experienced and can do it without thinking.
Horizons should always be level. Again, use the grid in the view finder, but ideally you should use a tripod to ensure (a) the capture is level and (b) you can use a remote shutter release to get a ‘shake free’ image. This will ensure your image stays in focus and you can also fire of a few in quick succession without moving the camera. There are even mini tripods for table tops or bendy leg tripods for placing on uneven surfaces designed for mobile phones and smaller cameras. This helps especially if it is a windy day!
Try different apertures for the same shot. This will change the focus and you can decide which is more interesting for different subjects.
Also think about tones. I am a bit of an amateur artist so this has been drilled into me by various art teachers. Two colours may seem to be different but in black and white their tones may be exactly the same. You don’t need a ‘posh’ camera to take great photos.
I have enclosed some of my own favourite landscape shots.