In addition to simply admitting to and asking to be forgiven for the sin
you'd committed (the third component of teshuva), you'd also be expected
to understand that you've likely committed many others. And not only
blatant ones, but subtle sins, too; since everything we do and say can
either do quiet and tender good or set off subtle noxious chords in others
and be suffused with self-indulgence. So you'd need to admit to and ask to
be forgiven for those sins as well.
You'd likely remember them all the time and would fast and mourn in
anguish; you'd spend the long cold night praying to, beseeching, and
pleading with G-d to forgive you and to restore your spiritual well-being.
And you'd be prone to persuading others to better themselves, too, like
someone with a dread disease he'd brought on himself, who now knows how
foolish he'd been and wants others to know also.
And when it comes to taking it upon yourself never to commit the sin in
question again (the fourth and final component of teshuva), you'd do well
to consider the pro's and con's of sinning. As Ibn Pakudah puts it, that
comes down to "weighing the immediate but fleeting and mixed pleasure
you'd get from committing a sin against the eventual, permanent, constant,
pure and unadulterated pleasure you'd get from fulfilling a mitzvah. Then
weighing the quick, short-lived, impermanent woe you might suffer
fulfilling a mitzvah" as when you'd visit the sick, perhaps, or attend a
funeral, etc. "against the eventual, constant, endless woe you'd suffer
for committing a sin".
That would undoubtedly move you to dwell upon your own mortality and
what's to follow in its wake if you abandon G-d, who'd been so incessantly
loyal and kind to you; and you'd want to be sure that all your debts had
been paid to others you might have inadvertently (or purposefully) stolen
from -- perhaps even from G-d Himself, so to speak, in your lack of
gratitude. And the latter would humble and discomfit you deeply.