Focus on grades or coursework
No one cares about grades in grad school.
There's a simple formula for the optimal GPA in grad school:
Anything higher implies time that could have been spent on research was wasted on classes. Advisors might even raise an eyebrow at a 4.0
During the first two years, students need to find an advisor, pick a research area, read a lot of papers and try small, exploratory research projects. Spending too much time on coursework distracts from these objectives.
Learn too much
Some students go to Ph.D. school because they want to learn.
Let there be no mistake: Ph.D. school involves a lot of learning.
But, it requires focused learning directed toward an eventual thesis.
Taking (or sitting in on) non-required classes outside one's focus is almost always a waste of time, and it's always unnecessary.
By the end of the third year, a typical Ph.D. student needs to have read about 50 to 150 papers to defend the novelty of a proposed thesis.
Of course, some students go too far with the related work search, reading so much about their intended area of research that they never start that research.
Advisors will lose patience with "eternal" students that aren't focused on the goal--making a small but significant contribution to human knowledge.
In the interest of personal disclosure, I suffered from the "want to learn everything" bug when I got to Ph.D. school.
I took classes all over campus for my first two years: Arabic, linguistics, economics, physics, math and even philosophy. In computer science, I took lots of classes in areas that had nothing to do with my research.
The price of all this "enlightenment" was an extra year on my Ph.D.
I only got away with this detour because while I was doing all that, I was a TA, which meant I wasn't wasting my advisor's grant funding.
Perfectionism is a tragic affliction in academia, since it tends to hit the brightest the hardest.
Perfection cannot be attained. It is approached in the limit.
Students that polish a research paper well past the point of diminishing returns, expecting to hit perfection, will never stop polishing.
Students that can't begin to write until they have the perfect structure of the paper mapped out will never get started.
For students with problems starting on a paper or dissertation, my advice is that writing a paper should be an iterative process: start with an outline and some rough notes; take a pass over the paper and improve it a little; rinse; repeat. When the paper changes little with each pass, it's at diminishing returns. One or two more passes over the paper are all it needs at that point.
"Good enough" is better than "perfect."
Chronic perfectionists also tend to be procrastinators.
So do eternal students with a drive to learn instead of research.
Ph.D. school seems to be a magnet for every kind of procrastinator.
Unfortunately, it is also a sieve that weeds out the unproductive.
Procrastinators should check out my tips for boosting productivity.
Go rogue too soon/too late
The advisor-advisee dynamic needs to shift over the course of a degree.
Early on, the advisor should be hands on, doling out specific topics and helping to craft early papers.
Toward the end, the student should know more than the advisor about her topic. Once the inversion happens, she needs to "go rogue" and start choosing the topics to investigate and initiating the paper write-ups. She needs to do so even if her advisor is insisting she do something else.
The trick is getting the timing right.
Going rogue before the student knows how to choose good topics and write well will end in wasted paper submissions and a grumpy advisor.
On the other hand, continuing to act only when ordered to act past a certain point will strain an advisor that expects to start seeing a "return" on an investment of time and hard-won grant money.
Advisors expect near-terminal Ph.D. students to be proto-professors with intimate knowledge of the challenges in their field. They should be capable of selecting and attacking research problems of appropriate size and scope.
Treat Ph.D. school like school or work
Ph.D. school is neither school nor work.
Ph.D. school is a monastic experience. And, a jealous hobby.
Solving problems and writing up papers well enough to pass peer review demands contemplative labor on days, nights and weekends.
Reading through all of the related work takes biblical levels of devotion.
Ph.D. school even comes with built-in vows of poverty and obedience.
The end brings an ecclesiastical robe and a clerical hood.
Students that treat Ph.D. school like a 9-5 endeavor are the ones that take 7+ years to finish, or end up ABD.
Ignore the committee
Some Ph.D. students forget that a committee has to sign off on their Ph.D.
It's important for students to maintain contact with committee members in the latter years of a Ph.D. They need to know what a student is doing.
It's also easy to forget advice from a committee member since they're not an everyday presence like an advisor.
Committee members, however, rarely forget the advice they give.
It doesn't usually happen, but I've seen a shouting match between a committee member and a defender where they disagreed over the metrics used for evaluation of an experiment. This committee member warned the student at his proposal about his choice of metrics.
He ignored that warning.
He was lucky: it added only one more semester to his Ph.D.
Another student I knew in grad school was told not to defend, based on the draft of his dissertation. He overruled his committee's advice, and failed his defense. He was told to scrap his entire dissertaton and start over. It took him over ten years to finish his Ph.D.
Aim too low
Some students look at the weakest student to get a Ph.D. in their department and aim for that.
This attitude guarantees that no professorship will be waiting for them.
And, it all but promises failure.
The weakest Ph.D. to escape was probably repeatedly unlucky with research topics, and had to settle for a contingency plan.
Aiming low leaves no room for uncertainty.
And, research is always uncertain.
Aim too high
A Ph.D. seems like a major undertaking from the perspective of the student.
But, it is not the final undertaking. It's the start of a scientific career.
A Ph.D. does not have to cure cancer or enable cold fusion.
At best a handful of chemists remember what Einstein's Ph.D. was in.
Einstein's Ph.D. dissertation was a principled calculation meant to estimate Avogadro's number. He got it wrong. By a factor of 3.
He still got a Ph.D.
A Ph.D. is a small but significant contribution to human knowledge.
Impact is something students should aim for over a lifetime of research.
Making a big impact with a Ph.D. is about as likely as hitting a bullseye the very first time you've fired a gun.
Once you know how to shoot, you can keep shooting until you hit it.
Plus, with a Ph.D., you get a lifetime supply of ammo.
Some advisors can give you a list of potential research topics. If they can, pick the topic that's easiest to do but which still retains your interest.
It does not matter at all what you get your Ph.D. in.
All that matters is that you get one.
It's the training that counts--not the topic.
Miss the real milestones
Most schools require coursework, qualifiers, thesis proposal, thesis defense and dissertation. These are the requirements on paper.
In practice, the real milestones are three good publications connected by a (perhaps loosely) unified theme.
Coursework and qualifiers are meant to undo admissions mistakes. A student that has published by the time she takes her qualifiers is not a mistake.
Once a student has two good publications, if she convinces her committee that she can extrapolate a third, she has a thesis proposal.
Once a student has three publications, she has defended, with reasonable confidence, that she can repeatedly conduct research of sufficient quality to meet the standards of peer review. If she draws a unifying theme, she has a thesis, and if she staples her publications together, she has a dissertation.
I fantasize about buying an industrial-grade stapler capable of punching through three journal papers and calling it The Dissertator.
Of course, three publications is nowhere near enough to get a professorship--even at a crappy school. But, it's about enough to get a Ph.D.