How can I get my voice back after laryngitis?

Depends. Majority of the time, the voice will fully recover after a bout of acute laryngitis. If it does not, i would encourage having your throat and vocal cords examined to rule out any other worrisome pathology, especially if you are a smoker.
Rest. There are several techniques to help your vocal chords recover. Rest them! they recover much more quickly with no speaking at all while healing. Breathe in steam from hot tea or over a bowl of boiling water with a towel over your head. Take a hot shower and breathe in the steam. Sip hot tea, especially herbal tea. Good luck.