I found a very informative Article about the common mistakes made when optimizing PPC Campaigns from Alan Mitchel.

5 Common PPC Optimisation Mistakes

Youíve researched hundreds of long-tail keywords, organised them into granular ad groups, and crafted ad messages which closely match the ad groupís keywords. You then set your Google AdWords campaigns live.

But after a while, you realise your PPC campaigns are not delivering the desired return on investment. You start making changes to bids, budgets, and keywords. Still no improvement, so you make more changes.

And so on.

Itís not long until youíve lost track of whatís working and whatís not. Your keywords and ad groups become disorganised, your Quality Scores start to fall, and you start paying excessively high CPCs to chase after visitors and sales.

If any of this sounds familiar, perhaps you need to take a step back and review your campaign optimisation strategy. Are you making intelligent and informed decisions based on reliable, insightful, and unbiased data? Or are your bids being changed and keywords paused in a random and haphazard fashion in a drastic effort to improve results?

Below are 5 optimisation mistakes Iíve found myself guilty of from time to time, and some tips on how to avoid these common pitfalls.
Read the full article here: 5 Common PPC Optimisation Mistakes