Problem Words
annex – connect, annexation – connection
invert – reverse, inversion – reversal
degrade – regress, degradation – regression
destroy – construct – construe
progression – progress, aggression – attack
topical – actualize
overlook – overhear
proceed – precede
reception – acceptance
pressure – impression, compression, depression etc.
critical, critic – theoretical, theorist/theoretician
genetic, geneticist – logic, logician
conscious, consciousness – subconscious, subconscious
agronomy, agronomist – astronomy, astronomer
feminism, feminist (adj.) – narcissism, narcissistic
demean – demeanor

Right
the Green (political party)
cannot
occurred
occurrence
criterion, criteria
phenomenon, phenomena
these data (no singular)

Wrong
the Greens (political party)
can not
occured
occurence
this criteria, these criterias
this phenomena, these phenomenas
this data

An interesting phenomenon is the often seen confusion of nominative and accusative/dative. Native speakers of English are sometimes not aware anymore of this difference and say things like “for you and I” – probably because they were told at school that “me” should not be used for the first person singular.
So now they don’t use it ... Even if it is the only correct form.
Saying “for you and I” is the same as saying “give the apple to I”. Not even the biggest moron would say that.
Examples of correct usage:
You and I should have a word with one another (nominative).
Nobody has heard of you and me (dative).
For you and me this should be no problem (accusative).

Another very common mistake in American speech is the question “where are you at?” instead of “where are you?”. This would only be correct, if one could say “at where are you?” – but one cannot.