This question is rather ambiguous since Puck applies the magic potion to more than one person's eyelids in A Midsummer Night's Dream. Of course, the first creature in whose eyes the "liquor" is dropped is Titania after Oberon devises a plan of revenge against his queen. As Puck is gathering this love potion, Demetrius disturbs Oberon as he flees from the pursuing Helena. When Puck returns, Oberon says he will "streak her eyes" and make Titania "full of hateful fantasies." He also tells Puck to take some of the potion and search the grove for an Athenian lady who is in love with a "disdainful youth," making him chase her instead. So, he instructs Puck to place the liquor upon the Athenian and
anoint his eyes;
But do it when the next thing he espies
May be the lady: thou shalt know the man
By the Athenian garments he hath on.
Effect it with some care that he may prove
More fond on her than she upon her love; (2.2.266-271)
When Puck goes into the woods, he does see Athenian garments; however, they are not worn by Lysander, but by Demetrius. In Scene 2 of Act II, Puck searches for the Athenian"
Through the forest have I gone,
But Athenian found I none,...
Night and silence.--Who is here?
Weeds of athens he doth wear:
This is he, my master said,
Despised the Athenian maid;
And here the maiden, sleeping sound,
On the dank and dirty ground....When thou wakest, let love forbid
Sleep his seat on thy eyelid....(2.2.66-81)
Later on, of course, Puck restores all the lovers to their rightful partners by getting Lysander and Demetrius and Helena and Hermia to fall asleep as he reanoints Lysander while Demetrius is also anointed, positioning them so that they will fall in love with Helena and Hermia respectively. He even removes the donkey head from Bottom with whom Titania has been made to fall in love. All of this supports the irony of Hermia's early remark, "O hell! To choose love by another's eyes" (1.1.142), and proves what Hermia tells Lysander in the first act:
The course of true love never did run smooth (1.1.136)
Puck applies the potion to a number of people in the play. But I assume that you are asking about the first time that he puts the potion on someone's eyes. The first time he does this (in Act II, Scene 2) the person he annoints is Lysander.
Oberon really wanted Puck to put the potion in Demetrius's eyes. He wanted Demetrius to love Helena as much as she loved him. But Oberon does not really describe Demetrius well and so Puck annoints Lysander instead. When Lysander wakes up, he sees Helena and falls in love with her.
Puck under orders from Oberon his master applies the juice of the magical flower "love-in idleness" on Lysander's eyes instead of Demetrius':
Lysander is fast asleep when Puck applies the magical potion and a little later is woken up by Helena who has been abandoned in the forest by Demetrius. Immediately to Helena's horror Lysander falls in love with her and begins woo her:
Oberon and not Puck applies the magic potion on the eyes of Titania:
Similarly it is Oberon and not Puck who applies the magic potion on the eyes of Demetrius: