Which users actions are worth logging, to gain better perspective on their behavior?

I am currently implementing a "User action log", that will keep interesting actions of users within our system.

Any advice on what to log? Of course, the answer is "everything you feasibly can", but I want to focus on the important actions, that will help us gain true insights.

Log every button click? Every hover on a button? Same for hrefs? What else?

Note:

1. The goal is better UX - we want to study our users, understand how they behave, and build a better system for them.



2. I'm aware of some 3rd party solutions that track everything users do, starting from Google Analytics, through apps like Clicktale. I'm not saying we won't use those - but still, a custom log with some select actions might provide extra value over these "log everything" type of systems.


3. The focus is websites, built for consumption over standard computers (mobile/tablet clients are less relevant for us a.t.m).

Answer

No no no! The answer is not "Everything you feasibly can"!

You really need to turn the situation around. There is no need to log user actions just to be sure. You need to know what you want to know more about. What is the purpose of this data collection?

1. Start out by defining some goals. What do you want to know?


2. Then you need to figure out what to look for to answer those questions.


3. 
   
   

   Finally you need to pick some key indicators you can log to feed your metrics/measures.

   
   

   (Take a look at the GQM method. This is a very handy method when you need to figure out what to measure/log.)

   
   

BTW, the log information does not (necessarily) provide you with valuable information alone. I don't know how many times I've accidentally hit the F1 button when I really aimed for the ESC button. What does these data tell you. Say you have 95% of the users hitting the help-button once or twice during a session. Did they intend to get help? Did they accidentally hit the help-button? Is the help button helpful to these users or is the form/page itself confusing?

What you need to do is to observe users in action. This is the best way to improve the UX of your product.