How can I learn to get collocations right?
Solution 1:
Because the basis of collocations is probabilistic, based on the colloquial, and the rules are arbitrary, it seems there is not actual 'getting it right', but rather there would mostly just be a 'sounds okay.' Note the computer example (powerful vs. strong computer); it's not that strong computers don't exist- they are just normally referred to as powerful.
Since this isn't idiomatic (ie, a static, limited case use), the problem with giving hard, fast rules is that they would likely be localized or a compendium of adjective/noun combos you would need to memorize.
For consolation, someone from the west coast of America might says something is 'totally awesome' and someone from the Atlantic northeast might says that same thing is 'wicked awesome'; but they'd both sound like fools because everybody knows that something is 'freaking awesome' here in Ohio.
Solution 2:
Google is your friend here. "Highly happy" returns 74,000 hits (many of which refer to a book with the phrase in the title), while "extremely happy" returns over 6 million. So the latter is clearly the stronger of the collocations.
Alternatively, you could use a collocation dictionary such as those published by Oxford or LTP.