Ibn al-Qayyim (rahimahullah) says in his book Madarij as-Salikin that Iblis tries to misguide humans through 7 gates ('aqabahs):
- Innovations (bid'ah)
- Minor sins
- Major sins
- Busying with permissible deeds to the exclusion of rewardable deeds
- Busying with deeds of lesser reward instead of greater reward
- And finally by unleashing the shayatin from among the jinn and humankind upon that person.
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.