I have picked 3 different album artworks from 3 different bands, representing 3 different genres -pop, alternative and heavy rock/metal.
Each follow different conventions but also share a few.
One Direction
This is One Direction's "Up All Night" album cover. The cover clearly shows the members of the band outside enjoying themselves. This is because this is what the audience wants to see from the band members. They want to see them having fun, being friendly and approachable and they essentially want to see them "up for grabs" as single boys. The colours are bold and bright and make the artwork appealing overall. It suits the target audience well and the other One Direction artworks follow a similar theme.
Gorillaz
The Gorillaz album artwork for "Demon Days" follows similar conventions, it shows the 4, albeit fictional, members of the band, just like one direction and it shows their personality and reflects their music. the artwork is important to the band because they first developed as a visual project as well as a band. The pictures of each band member are important. They all seem cool, distant and as if they don't care, which is part of their look. This album was aimed at the older generation, where being distant and cool was band of every band members image.
A Day To Remember
This album cover for A Day To Remember's "Homesick" is entirely concept design artwork, created by the band members. It's a visual representation of what the band feels there music is. It ducks conventions, like most metal albums. It doesn't show the bands members or relate much to the album name or songs. With Gorillaz it's distant and dark, One Direction is happy and party like but A Day to Remember's is purely what the band wanted to put. It doesn't advertise the band, it doesn't even have the name of the album, it merely it's more about the music that's inside.