What personal finance tips should a graduate (PhD) student know or take advantage of?

earning a modest PhD stipend (i.e. ~$25k).

Open a Roth IRA, since considering the $12,000 standard deduction you'll be in the 12% marginal tax bracket.

Because your future wages will probably be higher, now is the time to invest "taxed" money which will grow tax free for decades.

It's perfect for young, low-income people.

over general financial wisdom which may apply more broadly (e.g. opening an IRA

Ah, well... ignore what I just wrote.

Make sure you understand how grad school tuition, fees, scholarships and stipends work with the available tax credits, and deductions. You don't want to wait until April to discover that you should have done something different last year. Search your school website for an office that can help.

See if your state has any programs regarding tuition.

If you are about to start the program, or have already started, a key feature of a 529 plan the ability to save over time is limited. Still some people have found that if the state gives a tax break it can be enough of a benefit to funnel the money through the program. Of course that depends on your income tax situation, and if your rate is zero then there is no state income tax to save.

If you were working full time, and now you aren't, make sure you know what you will do for health insurance. Options include COBRA, a policy through the school, ACffordable Care Act...