OK..
First you need to work on your inner-game. There are tons of online and books materials on that, on of the books I like the most; The Secret. You should find it on Amazon.
Work on your self esteem, do sports, have a hobby get into good shape dress well, love your self and take care of your self. Unless you do love your self and take good care of your self you can NOT do that to any other...Got it?!! When you become an Alpha male..your voice will deepen naturaly, you move dfferently, think different, feel different and act different. This is called Inner-Game.
Boost your testosterone (naturaly) with god training and diet. Eat eggs, lean meat, nuts, fruit and viggies and train well. You WILL FEEL the difference. Any good sport will do, weight training, boxing, full contact martial arts like Kuykushin Karate, Thai box (really great). or if you dont wanna get punched in the face all the time just stick to regual GYM weight training combined with cardio sessions.
Then comes the last part; practice a deep voice, talk a little bit slower than normal. Also, go approach a 100 girl and DO GET REJECTED, the sorrow of it is guranteed to make you a better Alpha male and thus depen your voice. Just be nice no matter how rude the woman is..Be a Gentleman. If she slaps you, thank her and leave immediently (what worse could happen????????!!!!!!!) Got it??!!
Good Luck