There’s really no hard rules about this.  It’s a little tricky to balance the desire to express gratitude with not wanting to give the impression of bribery or overpayment.  You can show your appreciation with a simple thank-you card, or you can send some sort of tangible gift like flowers, chocolate, or even a movie ticket, or a donation to a charity in their name.  
Alternatively, a good way to show your appreciation is to call or email the doctor and thank them for their service, even if you don’t have a particular gift in mind.  But if you want to show your gratitude in the form of a gift, the last thing you want is to make the doctor feel obligated to reciprocate.  If you do want to give the doctor a gift, it should be something that’s meaningful to you personally and reflects your values and preferences.  Even if you did want to give the doctor a gift or some other appreciation, I wouldn’t suggest buying an expensive gift or restaurant meal to show your gratitude.
assitant
Flowers, fruit, or an article of clothing or clothing accessory are typical gifts that express appreciation.
assistant
how can i show appreciation for my doctor?
user
It’s always good to express your appreciation to a doctor.  If you feel particularly thankful or grateful, you can send a gift or a card to show your appreciation.
assistant
what sort of gift?
user