Not forgetting one's own conduct when warning others

An intelligent and experienced person well acquainted with the
Qur'an can detect the minor faults and weaknesses in the faith of
people and advise them.
This is a praiseworthy quality, yet that does not mean he himself is
free of mistakes. On contrary, he must strive to avoid committing
the same errors; otherwise, he may earn Allah's disapproval rather
than reward for his advice.
It is unlikely that someone able to recognize a fault in others
will fail to recognize it in his own soul. Undoubtedly, he is also
aware of his own wrongdoings and sins.
For instance, it would be hypocritical for a liar to call people to
truth and sincerity, or for someone who does not pray to call others
to regular prayer. An advisor who fears Allah would surely be the
first one to avoid committing sins.
In the Qur'an Allah reveals this fact as:
Do you order people to devoutness and forget yourselves, when you
recite the Book? Will you not use your intellect? (Surat al-Baqara;
44)
The conclusion to the verse above, "Will you not use your
intellect?" makes it clear that people should practice what they
preach.
Deviant attitudes such as the desire to control others, have one's
word respected or be influential underlie hypocritical behavior
that lies outside Qur'anic morality.
When someone counsels and advises only to attain status, respect and
esteem, the manipulation of faith- related issues for personal
benefit will only lead to great disappointment in the Hereafter.
When a believer sees another committing an error that he himself is
guilty of, he can let him know that he too is trying to correct that
same mistake. Then the two can encourage one another toward
improvement and by doing so, earn the pleasure of Allah.