what are the rules if any

This is non-standard speech.

Not that many rules

You just have to watch and use the patterns which are mostly

In my opinion, It is a kind of informal usage.

BelieverHi,

I see the contract form of a word being used so many times like the ones below. How can we use them properly?

kickin' the can

yo' leg

This form of English is considered “Ebonics” which originated in the South and is spoken by many African Americans in the Un

Dropping the g in the -ing forms is not exclusively associated with African Americans. Many whites, particularly in rural areas, also drop the g.

CJ

It's very common in some British English accents too.

CalifJimDropping the g in the -ing forms is not exclusively associated with African Americans. Many whites, particularly in rural areas, also drop the g.

CJ

Not just dropping the "g" from the present participle form of a verb. That's child's play!

What I referred to was words and phrases like the following:

Not just dropping the "g"

Yes, I realize that. But you were commenting on two examples, one of which was kickin', and I wanted to make sure that our forum readers were aware that this particular usage extended beyond the African American community.

Thank you.

Do you know if there are any rules or at least some sets of guidelines in regard to this area of the English language. Not only do I see so many of this type of usage being used in informal e-mail messages, I don't know it is the same type, but when I looked at some hymns written long ago, it exihibited what look to be similar uses.

is giv'n

sweeping o'er my s

Words are sometimes contracted in music simply because there is only one note of music available for two syllables of a word.
You should not use hymns or the Bible as examples of or guidelines for modern writing. Generally speaking, you should avoid contractions of any kind in formal written correspondence.