What are the rules for English word formations?

An overview of some rules for word formation in English is
offered
below.

Compounding
Frequent
collocations over time and with usage become double- or triple-word compounds that with
further time and usage become hyphenated compounds that with further time and usage
become single-word
compounds.

Blending

Usually the first syllable of the lead word and all or most of
the second word are used for forming words though blending, like electronic
mail blended to the blend compound e-mail, which is
rapidly becoming a single-word blend compound email.

Back formation

Back formations are formed by removing a morpheme incorrectly
perceived as a derivative suffix to create a new word, as in the removal of
-ar from burglar to form
burgle or the removal of -or from
editor to form
edit

Combining
Forms
The most common combining forms are Greek or Latin, which
are derived from nouns or adjectives or verbs, that combine with other combining
forms.

Derivatives
Derivational
prefixes rarely change word class and often indicate negation (e.g.,
un-, in-, non-) or relationship (e.g., im-,
pre-).
Derivational suffixes are used
within careful guidelines and often change word class. Some examples
are:
-ism, used on Greek loanword verbs to form
action nouns (e.g., realism).
-able, a Latin
suffix with the meaning of "capable of, tending to, etc", appears on Latin loanwords
(e.g., laudable) and on other words in English (e.g., teachable) and is adjective
forming.  
-ation, a combination of Latin
suffixes -ate and -ion, is used to forms nouns
from stems ending in -ate (e.g., separate) and on other English
words (e.g., starve).
-ness, an original English
suffix, from Old English and Middle English -nes, that forms
abstract nouns (e.g., goodness) from adjectives and
participles.

Some other suffixes are -ful, -fy,
-ify, -ise or -ize, -ist, -ity, -ly, and
-ment. A good dictionary will provide the specifics of etymology (origin),
usage and word class changes. Good online dictionary sources are href="http://dictionary.cambridge.org/search/british/?q=-ism&x=0&y=0">Cambridge
Dictionaries Online and href="http://dictionary.reference.com/">Dictionary.com.