A Matter of Choice...

British and American English have some distinct differences.
WHILE there are certainly many more varieties of English, American and British English are the two that are taught in most ESL/EFL programmes.
Generally, it is agreed that no one version is “correct”, however, there are certainly preferences in use. The most important rule of thumb is to try to be consistent in your usage.
If you decide that you want to use American English spellings then be consistent (i.e. The color of the orange is also its flavour – color is American spelling and flavour is British), this is of course not always easy – or possible.
The following guide is meant to point out the principal differences between these two varieties of English.

Use of the present perfect
In British English, the present perfect is used to express an action that has occurred in the recent past that has an effect on the present moment. For example: I’ve lost my key. Can you help me look for it?
In American English, the following is also possible: I lost my key. Can you help me look for it?
In British English, the above would be considered incorrect. However, both forms are generally accepted in standard American English.

Other differences involving the use of the present perfect in British English and simple past in American English include already, just and yet.
British English:
I’ve just had lunch. I’ve already seen that film. Have you finished your homework yet?
American English:
I just had lunch. I already saw that film. Did you finish your homework yet?

Possession
There are two forms to express possession in English - have or have got.
Do you have a car? Have you got a car? He hasn’t got any friends. He doesn’t have any friends. She has a beautiful new home. She’s got a beautiful new home.
While both forms are correct (and accepted in both British and American English), have got (have you got, he hasn’t got, etc.) is generally the preferred form in British English while most speakers of American English employ the have (do you have, he doesn’t have etc.)

The verb ‘get’
The past participle of the verb get is gotten in American English.
For example: He’s gotten much better at playing tennis. British English: He’s got much better at playing tennis.

Vocabulary
Probably the major differences between British and American English lies in the choice of vocabulary. Some words mean different things in the two varieties.
For example:
Mean: (American English – angry, bad humored, British English – not generous, tight fisted)
Rubber: (American English – condom, British English – tool used to erase pencil markings)
There are many more examples. If there is a difference in usage, your dictionary will note the different meanings in its definition of the term.
Many vocabulary items are also used in one form and not in the other. One of the best examples of this is the terminology used for automobiles.
> American English – hood
British English – bonnet
> American English – trunk British English – boot
> American English – truck British English – lorry
Once again, your dictionary should list whether the term is used in British English or American English.
For a more complete list of the vocabulary differences between British and American English, use this British vs. American English vocabulary tool at http://esl.about.com/library/vocabulary/blbritam.htm.

Prepositions
There are also a few differences in preposition use including the following:
> American English – on the weekend British English – at the weekend
> American English – on a team British English –in a team
> American English – please write me soon British English – please write to me soon

Past simple/past participles
The following verbs have two acceptable forms of the past simple/past participle in both American and British English. However, the irregular form is generally more common in British English (the first form of the two) and the regular form is more common to American English.
> Burn (burnt OR burned)
> Dream (dreamt OR dreamed)
> Lean (leant OR leaned)
> Learn (learnt OR learned)
> Smell (smelt OR smelled)
> Spell (spelt OR spelled)
> Spill (spilt OR spilled)
> Spoil (spoilt OR spoiled)

Spelling
The best way to make sure that you are being consistent in your spelling is to use the spell check on your word processor (if you are using the computer, of course) and choose which variety of English you would like.
Most dictionaries include both spellings and will make note of the two spellings. Usually the differences are noted in one of two ways:
In many US dictionaries the difference is included in the headword with the variation in parentheses ( ):
For example: colo(u)r
In British dictionaries, the dictionary makes note of the difference in brackets immediately after the headword i.e. colour (US color)
There are some general differences between British and American spelling. In British spelling, -our (honour), -re (centre), -ogue (dialogue), -ence (defence) and -ise (recognise) is used.
For American words, it is -or (honor), -er (center), -og (dialog), -ense (defense) and -ize (recognize).
American English spelling sometimes does not double the consonant at the end of a word, while British English spelling does, especially when the consonant is an ‘l’.
For example: travel, traveller, travelling (British) and travel, traveler, traveling (American). Also, jewel, jewelry (American) and jewel, jewellery (British).

Conclusion
In Malaysia, when writing or speaking in English, many people mix British English with American English (clearly heard from their pronunciations) and this include also statements heard or seen on TV, newspapers, magazines, books, labels and in notices almost everywhere including the various government departments.
Some common mistakes include using ‘practicing’ (American English), instead of ‘practising’ (British English).
Many write ‘color’ (American English) instead of ‘colour’ (British English) and ‘minimize’ (American English) instead of ‘minimise’ (British English).
Even many university and college students mix British English and American English when writing their thesis, dissertations, working papers, coursework, etc. and their lecturers don’t seem to care!
I think it would be good if Malaysians stick to British English.