Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
Participants should sign in by noon and pick up your registration materials
at the front desk.
The sentence switches from the third person to the second.
BETTER: Participants should sign in by noon and pick up their registration
materials at the front desk.
OR: Sign in by noon and pick up your registration materials at the front
desk.
For more on this, see "Agreement Between Pronoun and Antecedent"
on page 253.
Go to the "Options" menu to change the display colors, fonts, type size,
set predefined breaks in your program or open the dictionary.
The verb change is intended to apply to only the first three
elements, but there is no clear indication of where the next verb
takes over. The sentence seems to be saying that you can use this
menu to change the display colors, to change fonts, to change type
size and to "change set predefined breaks in your program"-the
last, of course, not making any sense.
BETTER: Go to the "Options" menu to change the display colors, fonts
and type size; to set predefined breaks in your program; or to open the
dictionary.
Customers may either pick up the merchandise themselves, or the
company will deliver it for a small fee.
Saying Customers may either implies that the customers will
be able to do one of two things-but then the focus switches to a
different actor, the company. The two options that follow either
must be parallel. Whenever you use the combination either/or, check
to see if the syntax still stands up if you put the second option in
place of the first. The sequence Customers may either the company
will deliver it for a small fee clearly doesn't work.
BETTER: Customers may either pick up the merchandise themselves or
have it delivered for a small fee.
OR: Either customers may pick up the merchandise themselves, or the
company will deliver it for a small fee.
He not only shoveled the walkway, but also the stairs and balcony.
The contrasted items that come after not only must be parallel.
Putting not only before the verb sets up an expectation that another
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