As Muslims we believe that devil is an entity that exists to misguide man kind till the day of judgement and as muslims our job is to prevent ourselves from falling into his traps and be obedient to Allah.
The question is how can a Muslim person know that he is being tricked by the devil into doing something wrong and save himself?
Ibn al-Qayyim (rahimahullah) says in his book Madarij as-Salikin that Iblis tries to misguide humans through 7 gates ('aqabahs):
A closer examination of these gates or levels (below) will show you how to recognize Iblis' whisperings and misguidance, and how to counter it. For all of these below, there is the knowledge component and there is the action component as well (acting upon the knowledge). Another thing to do, as Allah SWT says in the Qur'an and as @Kaveh mentioned in his answer, is to seek refuge and protection in Allah:
And if an evil suggestion comes to you from Satan, then seek refuge in Allah . Indeed, He is Hearing and Knowing.
If you look at the gates above, you will see that to cross the first gate successfully, one needs to have knowledge of their Creator, to ponder on His Signs, to know His Names and Attributes, to know and recognize His Lordship in their lives. With sufficient knowledge of Allah, one can protect ourselves from Iblis at this gate. To know that Iblis is misguiding us, just remember if any waswasa or whispering from Shaytan causes you to doubt your Lord.
To cross the second gate successfully, educate yourself on what the sunnah of the Prophet (saws) is and what opposes it. You know Shaytan is whispering to you and trying to misguide you when he tries to get you to oppose the sunnah.
To cross the third gate successfully, educate yourself on what constitutes major sins in Islam. You know Shaytan is whispering to you and attempting to misguide you when he tries to get you to commit major sins. He might say to you that belief is in the heart and sins have no effect on your faith - that's a sign he's trying to misguide you.
To cross the fourth gate successfully, educate yourself on what the minor sins are in Islam, and think not about what you think is the magnitude of the sin, but rather who it is against. If you're trivializing or justifying minor or major sins, that's Shaytan whispering to you. Avoid it by knowing what the sins are and why they are sins.
To cross the fifth gate successfully, you need even more education on which deeds to perform at what time. Shaytan attempts to busy you with deeds that are merely permissible to keep you from worship. If you find that happening to you, know that Shaytan is at work. Learn about which deeds you need to perform at what time. Playing games is permissible, but not as the cost of prayer or other obligations. Earning money is good, but not when it enters your heart and causes you to forget Allah.
To cross the sixth gate, you need to know even more fiqh: which deeds get you the most hasanat and strengthen your faith and worship the most. Staying up to read Qur'an until 3 AM may be good, but not if it makes you miss Fajr. If you find yourself arguing about Islamic topics or da'wah topics on the Internet, but not praying the prayers on time - Shaytan is at work. He might make you satisfied with your current deeds and discourage you from improving or adding on to them. Knowing fiqh will help in solving this.
I don't remember much about the seventh gate unfortunately, but I don't know anybody who needs to worry about that. It is the Prophets and Awliya of Allah who get there.
The first thing one can do is to ask God for protection as stated in verse 23:97 of Quran:
وَقُل رَّبِّ أَعُوذُ بِكَ مِنْ هَمَزَاتِ الشَّيَاطِينِ
And say "My Lord! I seek refuge towards you from the suggestions of Satan."
It does seem unlikely that one can always notice these unless one becomes one of "the mindful" ("مُتَّقین"). If you become one then verses 7:200-201 of Quran state that:
وَإِمَّا يَنزَغَنَّكَ مِنَ الشَّيْطَانِ نَزْغٌ فَاسْتَعِذْ بِاللَّهِ ۚ إِنَّهُ سَمِيعٌ عَلِيمٌ. إِنَّ الَّذِينَ اتَّقَوْا إِذَا مَسَّهُمْ طَائِفٌ مِّنَ الشَّيْطَانِ تَذَكَّرُوا فَإِذَا هُم مُّبْصِرُونَ
If a suggestion from Satan assail you, seek refuge with God; for He is hearing-everything and knowing-everything. Those who are mindful of God remember [God] when a thought from Satan assaults them, then they become clear-seers.
So the mindful see what is going on when Satan tries to trick them. You should be mindful of God and act as it would please him.
How can one become one of the mindful you may ask? In verse 2:21 Quran states:
يَـٰٓأَيُّهَا ٱلنَّاسُ ٱعْبُدُوا۟ رَبَّكُمُ ٱلَّذِى خَلَقَكُمْ وَٱلَّذِينَ مِن قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ
O people! Serve your Lord who has created you and those before you, perhaps you will be mindful [of God].
When we are about to do something or take an action, there is something inside our heart and mind tells us if this is good or bad, or uncertain,
for example before someone tries to steal or hurt somebody, his mind and his heart tell him that this is wrong, this is forbidden,
when the action we are trying is good, it will be clear.
Now it comes to the uncertain things, we should ask a Sheikh about it, if it is in doubt then it is better to leave it.
(حديث مرفوع) حَدَّثَنَا أَبُو نُعَيْمٍ ، وَعُبَيْدُ اللَّهِ ، وَيَعْلَى ، قَالُوا : أَخْبَرَنَا زَكَرِيَّا بْنُ أَبِي زَائِدَةَ ، عَنِ الشَّعْبِيِّ ، قَالَ : سَمِعْتُ النُّعْمَانَ بْنَ بَشِيرٍ ، يَقُولُ : سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ، يَقُولُ : " الْحَلالُ بَيِّنٌ وَالْحَرَامُ بَيِّنٌ ، وَبَيْنَهُمَا أُمُورٌ مُتَشَابِهَاتٌ لا يَعْلَمُهَا كَثِيرٌ مِنَ النَّاسِ ، فَمَنِ اتَّقَى الشُّبُهَاتِ اسْتَبْرَأَ لِدِينِهِ وَعِرْضِهِ ، وَمَنْ وَقَعَ فِي الشُّبُهَاتِ وَقَعَ فِي الْحَرَامِ ......."
There are four directions Satan may use to approach us: "Before them and behind them, from their right and their left." (7:17) (s)He who guards all these directions is safe from Satan's trickery.
Satan approaches from front by deceiving the individual with Allah’s mercy and forgiveness. (s)He makes the person feel at ease. (s)He, who is deceived by this delusion gets lazier in time, obeys less and less to the One and may refrain from spiritual practice.
Satan approaches from behind by the fear of indigence and its impact on the person’s family. Satan encourages person to stockpile more goods/property and be prepared for the future. By doing these, one ignores Allah. (s)He claims (s)he knows what is good for him/her, and builds his/her life on worldly reasoning. (s)He denies the fact that, whatever happens it is because Allah willed so.
Satan approaches from right by showing one’s virtues, knowledge, spiritual practices and his/her good deeds to himself/herself. (s)He, who is deceived by this delusion will be blinded from Allah by seeing his/her supremacy.
Satan approaches from left by calling people to sins, effrontery, lust and pleasure. “Nor wilt Thou find, In most of them, Gratitude (for Thy mercies).” (7:17) meaning ‘You won’t find them using their forces, bodies and benefactions in order to get closer to You.’
As said as a general instruction in the Hadith of Our prophet Muhammad (peach me upon him), Sins are those that usually perturbs your heart. The quotation is given below
Sin is that which causes doubts and perturbs the heart, even if people pronounce it lawful and give you verdicts on such matters again and again.
The most useful advise from me should be, Do not quickly conclude on things about their permissibility. I have seen unfortunately, many of my muslim brothers failing in that tricks. Do take appropriate action to make best judgement about their permissibility and go to the best person who know them. Don't just listen to your heart. If you take appropriate and sincere approach to know which is Haram and which is Halal, and then very unfortunately fall into haram, Allah might forgive you, since you take your precaution.
Again, Do not take the advice of your heart only. Always be prepared to go against your dearest will of your heart.
Another point that I want to tell you that, Don't be late on repentance, if you ever fall into evil. Quickly, and Very quickly revert to our most benevolent Lord, The Almighty, The forgiver of all sins, The very one who loves you most among all the things in this universe. Allah, always wants to forgive you. Don't think this, "I made a sin, and now, How can i shall want forgiveness from him?". Allah says in many verse in the Quran, here is one
وَإِنِّي لَغَفَّارٌ لِّمَن تَابَ وَآمَنَ وَعَمِلَ صَالِحًا ثُمَّ اهْتَدَىٰ
But indeed, I am the Perpetual Forgiver of whoever repents and believes and does righteousness and then continues in guidance.source
I read on a Book of Imam Gazzali (Kimiya-yi sa'ādat, The Alchemy of Happiness), That Saitan is very much distressed with the people in the age of Our prophet becuase, They do not even go to near sin, and also distressed with the later generation, because If they do sin, they quickly repent.
So, in short, Don't go near sin, and If you fall into sin unfortunately don't be late on repent. Here, near word is the most important.
Read the full hadith here
