I'm taking the PGRE this Saturday and after doing the practice tests I think the biggest issue for me is careless mistakes. Stuff like messing up some trivial algebra or arithmetic (for example writing 1/2 M R^2 w^2 as the rotational energy of a disk, forgetting that its 1/2 I w^2), misreading/misinterpreting a problem (reading three-dimensional oscillator as 1-d), and most stupidly, thinking one answer and absent mindedly bubbling in another.
For the algebra, I think it'll be most helpful if I write out my steps a bit clearly instead of just doing it in my head. And for numerical ones, not to choose an answer until I get one that pretty close to one of the answers. For the bubbling in the wrong answer I think it should be helpful if I both circle the answer on the test booklet and then bubble it in. The most useful strategy would be to have 20-30 minutes at the end to recheck, but that's not realistic given the time constraint.
Anyone else have such problems with stupid errors? How did you guys deal with it?