Iambic pentameter is the rhythm created between two syllables where the first syllable is un-stressed, and the second syllable is emphasized. Each line of your sonnet should follow this rise and fall from one syllable to the next. Sonnets are traditionally 14 lines in length. Commonly the fourteen lines are broken up into three quatrains followed by a couplet. A quatrain is a four-line group and a couplet is a two-line pair.
The rhyme scheme is set by the end word in each line of the sonnet. Each line may rhyme with the next line, or every other line may rhyme to create the rhyming pair. For example, if lines one and two rhyme, then lines three and for need to rhyme. Alternatively, if lines one and three rhyme, then lines two and four must rhyme to complete the pattern. Whatever rhyming scheme you set in your sonnet, it must remain consistent throughout your work.
A sonnet should include a turn, also known as a volta, where the action in the sonnet changes. You may change the theme of your writing, the tone of your sonnet, or the direction of your writing. For example, you may pose a series of questions to the reader at the beginning of your sonnet, then begin to answer the questions. Blank-verse sonnets intentionally omit the turn.