Say if you were a graduate of ABC university, and When you want to thank a teacher of this university because she used to help you a lot in some courses or because she has the same hobbies and interests as yours, and you want to be friends with her:
No gifts. Words speak volumes. If you must give gifts, something handmade is better than anything purchased. Purchased gifts, especially more expensive gifts, may, in fact make your instructor feel uncomfortable and skirts the line of appropriate teacher-student relationships.
At the very minimum, a handwritten, thoughtfully articulated note is the easiest way to thank a good teacher.
A handwritten letter to the department Chair is even more powerful, but the best way to thank a truly outstanding teacher is to nominate him or her for a teaching award. Most institutions have teaching awards that give excellent instructors public recognition, something to enhance his or her resume and best of all they sometimes come with a small monetary reward.
As a college instructor, the one thing that has meant the most to me in terms of thanks has been when students tell my superiors how much they enjoyed having me as an instructor. Even just an email to my boss from a former student was a very solid form of thanks. It made me look good; it also made my supervisor proud of himself for one of his lowlings having success. For me at least, this was the ultimate thanks.
A good thank-you note is always appreciated by a former teacher.
I would recommend that if you are a current student at the university, and may have that former teacher again, that you not purchase a gift with a significant price tag, as that could be viewed as creating a conflict of interest. On the other hand, a small memento of personal, but not monetary, value is still appreciated. (For instance, a photograph or small handmade item or perishable good would be OK.)
If you are an alumnus, then the rules are obviously different. However, before giving an expensive gift, you might want to consider if there's an alternate use of the money that might be even more appropriate or appreciated (e.g., a donation to a charitable organization in the teacher's name).
I'll suggest that you write a note. Use paper.
You can add a small gift to this - something that she can keep on her desk, a souvenir perhaps, that is related to her passion/subject.
Other than the great advice above, simply in terms of writing the thank you note, you may find this link useful:
http://www.artofmanliness.com/2008/10/23/the-art-of-thank-you-note-writing/
I'll mention the main points here, and you can use the link for a more elaborate guide.
a. Always write the note as soon as possible.
b. Send it through the mail.
c. Use real stationery.
When writing,
i) Begin by expressing your gratitude for the gift/service.
ii) Mention specific details about how you plan to use a gift or what you enjoyed about an experience.
iii) For some recipients, add some news about your life.
iv) Close by referencing the past and alluding to the future.
v) Repeat your thanks. (in short)
vi) Valediction.
I hope this is useful in penning the actual note. Cheers!
Sending a not very expensive gift but chosen carefully, with a personal note, as suggested above is good.
However, teachers often appreciate if students stay in regular contact with them, discussing future career/family plans and sharing updates about batchmates. It all depends on the kind of teacher and the level of your relationship.
It is traditional at the time of graduation to give your stole to someone who has provided you with an unusual amount of help and support. A lot of times this is given to one's parents, especially if they have paid for it, but it can also go to a mentor, as a profound expression of gratitude.
If you google "rate my professor", you will find some very popular websites that you can provide good feedback. Most of those who use such websites, are for giving negative feedbacks.
