Well-Formed Formulas

For a statement to be unambiguous and meaningful, it must be a well-formed formula (wff - usually pronounced "woof").  Just as in English, there are certain grammatical rules which a statement must meet if it is to make sense.  The general rule which each wff must meet is that every connective must actually connect two statements (or wffs) and do so unambiguously.  Specifically for the negation, every tilde must be followed by a complete statement.  Every symbolized statement is overall either a negation, a conjunction, a disjunction, a conditional, or a biconditional.

Examples
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2
3
4
~A∨B
~(A∨B)
~(A∨∨D)
~[F∨(G∨H)]∨I
This example is a wff.  The wedge has a statement to its left (~A) and a statement to its right (B), AND the tilde encompasses a complete statement (A).
 This example is a wff.  The wedge has a statement to its left (A) and a statement to its right (B), AND the tilde encompasses a complete statement (A ∨ B).
This example is not a wff.  The first wedge has a statement to its left (A) but to its right is (∨D), which is not a complete statement. 
This example is a wff.  The tilde encompasses everything in the brackets, which is a complete statement.  Every wedge has a complete statement to its left and its right (check it for yourself!)

Here are some more examples:

wff's
 non-wff's
~A • B
 ~(A ∨ B ∨ C)
G ⊃ (H ∨ J)
 ~(A ⊃∨ B)
~~~M • M
 Q ~∨ R
~(~A ⊃ ~B) ∨ ~(G ∨ ~F)
 ~A≡∨ B
Q∨~R
 B~

Make sure you understand why each of these examples is classified as it is!