It is very difficult to adapt to a style of music if it is not the style you like and that is why it is difficult to sing a particular genre of music if you do not like it. Some people are extremely versatile and can sing different genres of music or even inculcate different styles of music in one song. If you want to as versatile in blues and in singing blues songs, then you have to listen to a lot of blues music and practice a lot.
It is very difficult to say whether blues has any particular way to train someone to sing the blues. Neither can anyone teach you how to sing the blues nor does it have any one style of singing, so that you can practice and adapt to that one style. In fact, each blues singer has a different way of singing. Thus, you will have to listen to a lot of blues music and develop your own style of singing, but before that you have to understand what blues is all about. Blues is almost feel music, which means that you have to understand the lyrics and feel the song within you when you are singing. It is only way to get the blues style right since the songs are generally very sensual and smooth flowing. Your voice has to flow with the mood of the song and most of the times this is individualistic to a singer.
The first is of course, to listen to blues music by some of the best blues artists that have ever lived, like B. B. King, W. C. Handy, Bessie Smith, Charles Brown, Albert King and others. You have to stock on your collection of music albums. A good way is to download MP3’s to your computer and listen in your MP3 Player. Remember to understand, feel and criticize the music. Try to select a few songs which you like and include them in your daily practice sessions.
A very good exercise for blues style of singing is the Legato. Take any note and sing in a continuous but increasing or decreasing order of scales. It is as simple as singing “Ti..ii..ii…” You will get a better idea if you see some instructional videos of vocalists teaching how to sing Legato in a particular scale. Practice singing the Legato at least an hour every day and do this before beginning to sing.
As a last word, try to get a few friends who are interested in playing the blues, especially a guitarist and practice singing with them. Singing to the blues scale of music will help you understand the music better. Of course, singing blues is not easy, but if you really put your heart and soul into it, blues will flow out of you naturally. Blues has a very long, drawn out style of singing and that is why some people find it extremely romantic, so you have a significant advantage if you learn