[stylist] question about terminology

[Vejas Vasiliauskas]

Hi,
I had a question and was curious about your thoughts.
Lately, I have become very interested in British English from 
reading different books that take place in the UK and websites.  
I find it much more interesting to write words such as whilst 
instead of while and favourite instead of favorite.  And also 
words such as realise, socialise and practise.
I was wondering if, as an American,  it is appropriate to use 
them in my everyday writing (stories, school papers, etc?) It is 
English after all.
Thoughts?
Vejas