To the THES article, I can add having a viable research topic, having supervisors that whilst they don't do the project for you at least keep you on course, actually doing the necessary work to ensure a there is a viable, original contribution made, keeping a focus on the hypothesis or hypotheses you are trying to prove or disprove, not letting personal issues get in the way (difficult, I know), having the support you need (either professionally or personally) when the inevitable bout of depression comes, remembering to label and store your samples and data properly (that lesson is normally learnt early), etc.
I'm sure we can all add our own take on this. I note that article is from a Humanities-type angle and I'm sure Science and Engineering candidates can add their own thoughts to it.
Ian (Mackem_Beefy)