A:

Acrostic - An acrostic is a poem in which the initial or certain internal letters of the pieces lines spell out an additional message or name that usually adds further meaning to the piece, though not necessarily the case. Typically an acrostic uses the first letter of each line to spell out the message or name. But there are various other manners of creating an acrostic other than using the first letters. A message may be hidden by moving the letter one or more spaces over in successive lines. The message may also be placed in the last letter of each line or even a combination of methods to arrive at double acrostic poem.

Alliteration - Alliteration is the repetition of either consonant or vowel sounds within proximity such as a line or stanza. Repitition of consonant sounds is called consonance, while vowel repetition is called assonance. Typically most people associate alliteration with what's also called head or initial rhyme which uses the first or first couple letters. (i.e. alluring/angel -- where the "a" is repeated sound; callous/cat -- "ca" being the repeated sound/letters). But consonance and assonance can take other forms. Final alliteration is the using the last letters of words to make the alliterative sound. Parallel or cross alliteration uses multiple words, such as velvet petals/very pretty -- the 'v' and 'p' being consonants. Hidden alliteration uses consonants or vowels in the middle of words.

An overdone example would be any of the numerous tongue twisters such as "Sally sells sea shells by the sea shore." That is also a good example of why it is best to not over use this device as it can become distracting and difficult to read. In moderation however it can of course aid in the lyrical flow or add subtle emphasis to particular words.