Premise

I make a living developing web-based applications for all form-factors (mobile, tablet, laptop, etc). I make heavy use of SOA, and send and receive most data as JSON objects. Although most of my work is completed on the .NET or Java stacks, I am also recently delving into Node.js. This new stack has got me thinking that I know reasonably well how to secure applications using known facilities of .NET and Java, but I am woefully ignorant when it comes to best practices or, more importantly, the driving motivation behind the best practices.

You see, as I gain more prominent clientele, I need to be able to assure them that their applications are secure and, in order to do that, I feel that I should learn to think like a malevolent hacker.

What motivates a malevolent hacker:

1. What is their prime mover? What is it that they are most after? Ultimately, the answer is money or notoriety I am sure, but I think it would be good to understand the nuanced motivators that lead to those ends: credit card numbers, damning information, corporate espionage, shutting down a highly visible site, etc.
2. As an extension of question #1--but more specific--what are the things most likely to be seeked out by a hacker in almost any application? Passwords? Financial info? Profile data that will gain them access to other applications a user has joined?

Let me be clear here. This is not judgement for or against the aforementioned motivations because that is not the goal of this post. I simply want to know what motivates a hacker regardless of our individual judgement.

What are some heuristics followed to accomplish hacker goals?

Ultimately specific processes would be great to know; however, in order to think like a hacker, I would really value your comments on the broader heuristics followed. For example: "A hacker always looks first for the low-hanging fruit such as http spoofing" or "In the absence of a CAPTCHA or other deterrent, a hacker will likely run a cracking script against a login prompt and then go from there." Possibly, "A hacker will try and attack a site via Foo (browser) first as it is known for Bar vulnerability.

What are the most common hacks employed when following the common heuristics?

Specifics here. Http spoofing, password cracking, SQL injection, etc.

Disclaimer

I am not a hacker, nor am I judging hackers (Heck--I even respect their ingenuity). I simply want to learn how I might think like a hacker so that I may begin to anticipate vulnerabilities before .NET or Java hands me a way to defend against them after the fact.