Hm. Well, for singing in general... practice x 10232392093. lol. If you already do this (yay) you can add more exercises; do scales going lower as opposed to lower. Even if you cut out, keep going. Don't worry too much about your voice going weaker as you go lower on the scale... that's pretty normal. It'll hopefully start to get better as time goes by.
Keep in mind, I haven't done any serious lessons/singing lately, so there will definitely be more helpful advice out there. But I do this regularly, and it's helpful for all types of singing.
Oh yes, and you can go online and find some good...lessons, of sorts. YouTube videos and Podcasts are available too. ^^