This PDF contains three different 12 bar blue patterns in B flat that are progressively more difficult. It shows the blues scale and offers some suggestions on working to develop skills on using a "Walking Bass." Hope this is helpful to you!
Here is picture taken at a Improvisation workshop I led in Seoul, Korea on January 14, 2008 at Church Music Explosion, 2008 which was sponsored by Sunmin Music.
Are you looking for some more in depth help in learning how to play by ear? ...If so, then check out the book, "The Secrets to Playing by Ear," by Jermaine Griggs at the link below.
GospelPianoToday.com is another incredible site if you are looking for great DVDs that teach practical improvisation for contemporary gospel styles of music. A good choice!