What can be done to possibly avoid corrupt practices in the blind peer review process? During my short career as a researcher I observed a few seemingly unethical behaviors by Editors and Associate Editors:


being asked to include a particular new author in order to be accepted
being asked to cite articles with no apparent link with my article
being told by the conference TCP (one of the top conference) to reject all the articles I review
In one unique case, I reviewed an article and recommended strong rejection, it was subsequently accepted without revision. Reviewing the authors profile and handling editor, I found one of the author is an Associate Editor for another journal. It appears that both help each to publish articles in their journals.


All the above experiences were observed in well-reputed journals and conferences. Given all this, how what can I do to "clean this mess" in academic the journal/conference review process?
There is not a lot that you can do change the system. However, there are certain things you can do in the various instances you describe:


  being asked to include a particular new author in order to be accepted


If the person has no good claim to authorship, I would politely refuse such a request and explain why this person is not an author. If they refuse to publish your paper, then submit elsewhere.


  being asked to cite articles with no apparent link with my article


If there is no apparent link, then you can't cite it. I would respond with something like "We do not see how this article is related to our work. If the reviewer wishes to explain the relationship, we can include a citation."


  being told by the conference TCP (one of the top conference) to reject all the articles I review


There is little point in reviewing the papers if the decision has already been made. You can politely refuse the review request.


  In one unique case, I reviewed an article and recommended strong rejection, it was subsequently accepted without revision. Reviewing the authors profile and handling editor, I found one of the author is an Associate Editor for another journal. It appears that both help each to publish articles in their journals.


It's up to the editor to make the accept/reject decision, not the reviewer. Sometimes reviewers get it wrong and the editor has good reason to ignore their recommendation. However, it sounds like you believe this to be a case of corruption. There is little you can do about this other than refusing to have further interactions with these journals. You can tell others about what you have witnessed. Presumably others have witnessed it too. If news of this spreads, then it will (deservedly) harm the reputation of the editor.


  All the above experiences were observed in well-reputed journals and conferences. 


This is unfortunate. Such behaviours should bring journals and conferences into disrepute. 

On the individual level, you can choose where to submit your articles and which review requests to accept. There are many factors to consider when choosing where to submit. Of course, prestige is a big factor, as publications in prestigious venues helps advance your career. However, you can include reviewing practices as a factor. You can also refuse review requests from venues that you believe will ignore your reviews. And, if there are venues that you believe are doing a good job, you can support them by submitting and reviewing.

If enough people begin to avoid venues with questionable practices, then that will have an effect on them. Likewise, if people support venues with good practices, then those will go up in the prestige rankings.