I think the title 'Vixen' is very foxy and sexy and it is bold so it stands out.
There are three different fonts used, which is a traditional convention of a magazine. It varies the text, without over-complicating things.
Rihanna is a well-known artist, so she is a recognisable face to the audience. She is colour-coded to the magazine as the background is purple and she has purple in her hair. She protrudes off the page as she is in blue which stands from the purple background. This makes her the main focus of the front cover and it also makes her appear dynamic.
This front cover is not too cramped, but not too simple. There is only one image on the full front cover, which focuses all the attention on Rihanna. Having one image is a classic convention of a music magazine.
Rihanna is posing sexually, she has her mouth half open, is dressed quite revealing and has her hand on her hip with her head tilted.
An attractive female is used which supports Naomi Wolf's theory of having erotic images of women sell products to women.
Another convention of a music magazine is a website, this is so the audience can gather extra information about the magazine and it's contents on the internet.
The bar code can be placed anywhere, but in this case it isn't in focus as it's in the bottom corner, so it doesn't attract attention away from the rest of the front cover.
The colour scheme is particularly feminine: purple, pink and yellows. This tells me that the magazine is aimed at female's but also as it concentrates on celebrity lifestyle and not just the music.