How to compose my photos better and what are the rules that say a photo is better composed

A Good composition usually means having unity and balance in shapes, colors, and textures in your photographs.
Quite often you will find mood, emotion, and actions are often enhanced by flouting conventional photographic rules.

Hence any rules that I mention are just guidelines to make a photography look better (in other words "capture the eye of a viewer")

if what you did works, it works!! If it Doesn't .. it just doesn't.

Having said that there are some general you can use to make your images more captivating. SOme of them are 

Rule of Thirds (the easiest and most commonly used rule)
Remember there are similar ratios available such as (Golden ratio (grids separated at 1:0.618:1), Fibonacci Spiral )

You can also mix it with other techniques such as using
appropriate Lead (nose) room, Headroom for your subjects
Having Balancing elements

Some other things you can keep in mind are
Repetitions / patterns / symmetry in your photographs

Creating depth / sense of depth (you can make use of layers to achieve it for example)

Fill the frame, crop tight to enhance your subject

Leading Lines, Diagonals which you can capture

There are more such techniques.
Will make a blog post with examples soon and will paste a link here.

You could also try out Module-3 of our Basic Photography workshop (Basics2Advanced) 
artriva.com/photography-workshops/basics-to-advanced
For more in-depth / hands on understanding