There are several schools of thought on this subject and some will say you can use any format you like and that is true to a point. However if you intend to shop and attempt to sell your material, artists, agents as well as publishers will be paying close attention to whether your song meets the formula that has been selling when picking songs they will support. In my opinion following what has sold in the past and most importantly what is selling now is the best method to follow.
If you want to maximize your chances then follow one of these formulas below.
1. The AABA Song Structure
Songs in an AABA structure are built on two different sections. Section “A” is basically just like your common verse in a song and can be 4 or 8 lines long. There are two section “A’ parts back to back, each time with different lyrics. Section “Â” songs usually carry the title of the song in the first or last line of the section.
Section B is musically different and like a chorus bringing a sense of release from the musical themes. It often provides lyrical contrast too, developing a additional path to the storyline, or giving insight into a different part of the picture.
The Section “B” and its eventual return to another section “A” should sound inevitable and create a cohesive and satisfying musical package.
2. The Verse Chorus Song Structure
Songs in a Verse/Chorus structure also have a lot of contrast between the two sections, but there are several differences. Where an AABA song will tend to stand on it’s own pretty welll, a Verse/Chorus song will almost always feel incomplete without its Chorus. In the chorus the title of the song can be stated in the first and last line which tents to create a nice hook. Unlike an AABA song the chorus does not need to take a totally new musical direction. To hear some great examples or verse chorus songs with and without a bridge section listen to almost any Beatles song . The good chorus should create an urge in the listener to sing along, and is usually repeated several times at the end of the song with the title of the song being the last thing the listener hears.
3. 12 Bar Blues Song Structure
This is a very common song structure on your can hear in the music of all the blues greats like Buddy Guy, Lonnie Brooks, and Stevie Ray vaughn. It is based on a 12 bar musical progression and the lyris are usually very simple and repetitive. The bass guitar hass your typical walking blues bass line like in Steve Ray Vaughn’s song “The Sky is Crying” 
4. The Middle 8 Song Section
In music theory a middle 8 refers to the section of a song which has a significantly differentin melody than the rest of the song. Such sections often consist of a new chord structure but also frequently just alternates between two chords. Aa middle 8 occurs in the middle of the song and the length is generally 8 bars long. Aerosmith’s “I don’t want to miss a thing”  is a great example of a middle 8 song section
5. The Bridge Song Section
A Bridge section is not a song structure alone but is an added section like a middle 8 and is commonly seen in a Verse /Chorus song. Once again the Beatles used the ridge in many of their songs.
6. The Solo Song Section
A Solo is usually a repeat of a Section A, Section B, Verse or Chorus and is played nstrumentally instead of sung. It is very effective in ring a climax to a song and provides clear constrast even when it is musically similar to the other sections.
Until my next post here is to wishing you luck in all your songwriting ventures.