Well, I've read lots of your posts and most of them represent my thoughts about the principles of creating material.

Well, I've read lots of your posts and most of them represent my thoughts about the principles of creating material. Some of you have mentioned points I have never thought before, and I found that really helpful.
Now, as far as my way of thinking is concerned, that's not that different from yours.
There are numerous things we have to bear in mind before and while creating material. Here are some of the most important (to me : ))

- the aim/objective of the material

- the target group (age, level, needs, interests, personality, type of
learners etc)

- clear and easy to understand instructions

- appropriate difficulty level of the content (personally, I adjust
everything - vocabulary, grammar structures- according to CEFR)

- interesting topics (authentic and real ones are even more
interesting)

- appealing page layout (appropriate fonts - easy to read -, bright
colours, catchy images, no "crowding")

Thanks for reading! ; )