My experience of earning credits
When you join Wealthy affiliate you understand how important it is to earn credits. There are two main ways of earning credits. One , by giving feedback on websites and other by giving comments on a website. Feedback is commenting on the layout, images, widgets and so on. Comments are to be interactive about the content of the post or page. While commenting you have to comment on the content and what topic is all about and what you gain out of learning from the topic. While giving feedback you can give recommendations and suggestions about the website but same should not be done while commenting on a content.
Criticism sometimes is not taken positively so what you can do is see and write on whatever good you can view on the website. Whenever you open websites try to read comments to understand how well you can comment on the website in order to earn credits. Negative, criticising comments are always disapproved. It is a process a new comer has to learn, many times you cannot express yourself though.