Which is better in teaching grammar, to write the rule first then explain it by examples or to write examples first then explain the rule, and why?

Putting examples first is better..because in this way we will draw the students attention and make them more curious to know what it is about..and it is most efficient in some cases (depending on the nature of the rule) to let the students conclude the rule by themselves..then in the end we clarify the rule and fulfill what the students missed and regenerate it again for them in a rule form.

To write examples first then explain the rule is better way Bascially , students are not interested in learning the rule because it is so boring.
But if you use a good examples that make students pay attention to you will be a much better.

I think showing examples at first will lead the student for a better understanding of the rule. 

For a students perspective, I would prefer "rules first, then the examples".
Its because for someone to fully understand such thing the teacher must explain very well the rules so that they will have that full understanding regarding its rules.
Then giving examples that is part of realm or those which they themselves can relate with would be the next thing.
I do believe that by doing this, a teacher does his/her role in her most compassionate way that her student will surely learn and that they are not wasting their time and money.
This will help them have a thorough understanding and learning which they can use in their daily living.

It depends on the student whom you are going to teach; Infact both ways are good.

i would prefer by stating the rule first and then explaining it by giving examples.because when u put a rule in front of somebody ,most probably a student then the first thing which comes in ones mind is ,HOW?so to explain it u go forward by giving examples and further describing it and making it understand for others which is more suitable method than giving examples first which creates confusion in a student's mind that what is the main thing which actually a person wants to describe.so in my opinion stating a rule first and then illustrating and explaining it by giving examples is the better option.

Write the rules first then the examples

write the example first then as the student if they have an idea on what have writen on the board for just to refreshing their minds then explain it afterwards one by one explaination to the student until they can understand.

يمكن استخدام الطريقتين : وهما تمثلان الاستنتاج والاستقراء اذاكان الطلبة متمكنين من اللغة نستخدم الاستقراء من الامثلة الى القاعدة اوالقانون وهنا يجب توجيه الطلبة الى الشيء الذي نحاول التوصل اليه من خلال الكلمات ووضع خط او لون او خطعريض او قائمة اما اذا كان لدى الطلبة ضعف او مبتدئين نستخدم الاستنتاج من القاعدة الى الامثلة في في هذاه الحالة يجب التاكد من ان الطلبة على معرفة تامة بمكونات ومحتوى القاعده ثم كتابة الامثلة وبعد ذلك تحديد الامثلة المنتمية للقاعدة من بين مجموعة امثلة ثم الطلب من الطلبة اعطاء امثلة على القاعدة اوستخراجها من نص

using deductive method in teaching grammar is much better because students use the examples to reach the rule.
This makes them feel self esteem because they discovered the rule by themselves.

if the aim is to make ss communicatively competent, i would say that it's better to give examples first and let the students think about the rule, but if the purpuse is to be grammaticaly competent so as to succed in an exam for example then we can teach them grammar rules first.
  however,  research in linguistics and psycolinguistcs say that students do not learn by rules but by practising the language.
there are xcases where we can find ss who know an infinite number of rules but if we just ask them to consrtruct a sentence they fail.
in short, teaching a language inductively or duductivly depends on the structure that a teacher wants to to teach.
both methods can be used if the lesson ends by the ss being able to use what they learned in real situations.