I would suggest you learn how to compose landscape and portrait shots first, before breaking good rules and tilting the camera. When you find a subject or scene that you like, stop for a minute and decide what is important about what you see in front of you. If its a small detail and you want to keep a tight frame, zoom in and then leave the lens set at a certain focal length, now move around until you have a nice composition. Concentrate on where light is coming from and how it is affecting your subject, and take a look at everything in your frame, what needs to be there and what doesn't?
And please, don't rely on cropping a photo afterwards, it may turn a crap photo into an average photo, but you won't learn anything about composition by simply cropping later on, its a bad habit so kick it now. Get to know the format of your camera and work with its size, if you specifically want a square photo, then shoot an image with the camera but keep in mind you will be cropping out a 3rd of the shot afterwards.