This is a great question, and in preparing to help answer this meta-question for you, I went and looked again at the /ask page, and realized they have changed things since the last time I saw it (sad panda face). There used to be some great resources there that would help you focus your thoughts, but those being gone now, we'll break this down the best way I know:
Objective: You obviously want to know what to measure so that you can be objective and pragmatic, you don't want to black-magic measure. Some understanding of each option would be helpful, but if you're just given direction you can search the API docs (altho a link to the first one would be rather dandy).
Motivation: Indicating that you're obviously willing to tackle this yourself without being guided, which I think by asking if someone can link you to information on one data point being measured that you should be able to find additional ones. Being able to link to these yourself and asking if these are the right data points, establishing that you've done some leg work, will go a long way to getting people to discuss the right data points to monitor.
Establish what you've already done: You want to show that you've done some research on this. Come to the table with what it is you're wanting to monitor, and why you think that's important. Even if all you say is "We want to monitor the disk I/O and the network latency, because we think that's going to tell us if that's when are slowdown is occurring" or something. The point is, don't just throw your hands up in the air, come to the table like a professional who needs help, but has some semblance of order.
If you're following these basic guidelines, then even tho there are a lot of ways to respond to this question with valid answers, you're still going to be asking what a good SE Q is all about.
Do try and make it as specific to your case as is reasonable, so people don't spend a lot of time guessing what you've done. We don't need a generic "oh, look, here's all the options forever" as those are going to change over time. Let's answer your question today.
HTH, YMMV.
