start smokin with him and then tell him hes youre role model
give him the hard facts of what it does to you, have you been to the site whyquit.com..
have you told him your really depressed about it? i know how you feel, but i got my dad to quit. dont lose hope.
First off, you can't MAKE him do anything. 'you can lead a horse to water, but you can not make it drink...'
The best approach would be to get the whole family behind him to take the first steps ie deciding to quit in X amount of time. Provide incentives, get right behind him and the rest is all up to your dad.