How does Lord Henry try to influence Dorian Gray in A Picture of Dorian Gray?

Lord Henry meets Dorian Gray just as Basil is finishing his portrait of him and is much taken with his beauty and innocence. Lord Henry uses his way with words to try to corrupt Dorian. He tells him not to go into philanthropy but to pursue his own desires. However, Lord Henry is wily: he doesn't frame pursuing one's own desires as selfishness but as living out a higher ideal in life. Lord Henry says:

I believe that if one man were to live out his life fully and completely, were to give form to every feeling, expression to every thought, reality to every dream—I believe that the world would gain such a fresh impulse of joy that we would forget all the maladies of mediaevalism, and return to the Hellenic ideal—to something finer, richer than the Hellenic ideal, it may be. . . . Every impulse that we strive to strangle broods in the mind and poisons us. The body sins once, and has done with its sin, for action is a mode of purification. Nothing remains then but the recollection of a pleasure, or the luxury of a regret. The only way to get rid of a temptation is to yield to it . . .

In other words, Lord Henry takes advantage of Dorian's innocence to twist evil words and make it seem as if the highest good is to indulge in the lowest depravity. Dorian lacks the intellectual apparatus at this point in his life to adequately challenge Lord Henry, and he falls under his spell. Lord Henry is a master at manipulation and knows how to be quiet when he needs to be. After the above speech he is silent, and Dorian fills in the silence by thinking:

Life suddenly became fiery-coloured to him . . .

He is enticed and seduced by Henry's decadent philosophy, and before he knows it, has sold his soul to devil.

Lord Henry tries to influence Dorian Gray by encouraging him to lead a life of debauchery. His philosophy of life—if one wants to call it that—is little more than a self-serving cover for an indulgent, hedonistic lifestyle. Lord Henry, in common with many louche young rakes of his social class, is thrilled at the prospect of embarrassing his elders and betters, peddling wild, improbable theories of how to live one's life that are motivated by little more than an adolescent desire to shock.
There's no sense that Lord Henry believes in any of his nonsensical ideas, let alone chooses to follow them—but Dorian's different. He's young, naïve, and impressionable. Indulging in the kind of debauched lifestyle seemingly endorsed by Lord Henry is simply too hard for him to resist. If Lord Henry's debauchery exists purely on the theoretical level, for Dorian it is practical, with dangerous consequences. The lord may not be directly responsible for any of Dorian's sordid actions, but he certainly planted a seed in the young man's immature mind, and for that he must be held morally accountable.