A Shakespearean or English sonnet has fourteen lines, consisting of three groups of four lines each, followed by a single rhyming couplet. The rhyme scheme is abab cdcd efef gg. Every (or nearly every) line will have ten syllables, divided into five feet of two syllables each. Each "foot" is called an iamb and consists of one unaccented syllable followed by one accented syllable, like this: My mis | tress' eyes | are no | thing like | the sun. Each accented syllable is in bold, and the vertical lines mark the divisions between feet. This meter, consisting of the rhythm of the feet and the number of feet per line, is called iambic pentameter. "Iambic" refers to the rhythm of unaccented and accented syllables (each foot is called an iamb), and pentameter means that there are five feet (penta-) per line.

The three quatrains which make up the first twelve lines of "My mistress' eyes" are actually a list of all the ways in which the speaker's lover fails to measure up to things to which writers often compare their loves: the sun, coral, snow, roses, a goddess, and so forth. However, the volta, or turn, happens in the final two lines: the narrator declares that his lover is actually just as rare and special as any other love who is falsely compared to these things. Other speakers may lie and say that their lovers are like goddesses, but this is simply never the case. This narrator need not lie in order to glorify his lover.

Please see the links below for more answers.

In terms of structure, a Shakespearean sonnet has 14 lines and is written in iambic pentameter.  This means that is has 3 quatrains (4 line sections) and one heroic couplet.  The rhyme scheme, therefore, is abab (quatrain 1), cdcd (quatrain 2), efef (quatrain 3), and gg (heroic couplet).

Like a Petrarchian sonnet, Shakespeare usually presents a problem in the first octet (8 lines) and a solution in the sestet (6 lines) with a volta (a turn) in line 9 which transitions from problem to solution. 

There are some exceptions to this break down.  Sometimes only the couplet can contain the solution.  In Sonnet 116, for example, Shakespeare gives the solution early ("it is an ever fixed mark") and develops his answer throughout the sonnet.  In any case, most of Shakespeare's sonnets deal with the themes of eternity (of art and artist).  Here are a list of other questions to ask yourself:

1.  What is happening in each quatrain?  Are there shifts between each quatrain?  Do the quatrains build on each other?

2.  What purpose does the couplet serve?  Is it a conclusion, or does it restate a message in the sonnet, only in stronger terms?  Does it refute anything from the above 12 lines?  What finality does it provide?

3.  Does the sonnet begin with an image or "scene" from the external world?  Does it use an extended metaphor throughout?

4.  How does the sonnet form a wholeness from the sum of its parts?  What is the speaker's overall message?  Does this message resonate in the internal and external world?

Also, here's what I have from a set of killer lecture notes I've used in the past: (see link below)

http://faculty.ncu.edu.jm/castillo/Class_Notes/Major_Authors/Shakespeare's%20Sonnets%20%20Synopsis.doc