So, if you're at an institution that gives TA support for grad students (i.e. almost every institution), make sure you know the procedures and timing for requesting your people get put into the TA support pool.
I realized today (when the TA assignments got emailed around) that in our department, PIs have to request that first-year students get put on the list before they've even officially joined a lab, just before the end of their final rotations... so somewhere along the line I was supposed to know that! But I never asked, I kind of just assumed they were magically supported by TAships or somehow during their first year while their status in a lab was still kind of in limbo. Luckily for me, some administrative scrambling has ensued to rescue my screwup and make sure my student will be supported next semester, but this is not the kind of mistake it is a good idea to make too many times before you come up for tenure.
So LESSON OF THE DAY/SEMESTER: Don't assume anything about TA support, it makes an ass out of (pretty much just) you.