A big part of managing GRE timing is understanding how the folks at ETS think about the test, and trying to identify concepts accordingly. The GRE hasen't changed all that much in the decades they've been around, so if you can anticipate what's coming, you can buy yourself a lot of time. How you do that depends on the section, of course--but here's some general strategies.

In the Quant sections, don't just do the math--but try to articulate what concepts are being tested, how you can simplify expressions or extract key data from word problems, and maybe two or three strategies that may be applicable.

Here's the way I break it down:
QUANTITATIVE

1) Read the question carefully; make sure you know what's being asked!
2) Identify key concepts. What's being tested?
3) Simplify/extract key info. Write it down, draw it, whatever helps!
4) Assess difficulty. I like to categorize problems as Difficulty level 1 through 4:
1 is easy
2 is doable
3 is tough but you have some ideas
4 is either very difficult, or you can't see a shortcut to getting the answer in time.
It's ok to come back to a 3 or a 4; take your best guess, flag it, then return.
5) Look for clues in the question and the answer choice.
6) Select your strategy: try your own numbers? work backwards from answer choices? estimate? Just do the problem straight?
7) do the math!

VERBAL:
Reading Comprehension
1) Structure is more important than detail. Don't worry about remembering details--you can always get them if needed!
2) Read for tone, differing points of view, and identify passage scope.
3) Read ACTIVELY--not PASSIVELY. Look for structural/tonal clues. If certain words/phrases jump out at you, they may be important

For vocabulary-oriented questions, try to get a sense of the general tone of the sentence, and look for key words that can clue you in to the direction/flow/tone. Try to determine whether the words are positive, negative, or neutral in tone--that can help you narrow them down.

And finally, as you practice, do timed drills! They don't have to be full test sections--sets of 10 or so questions each work well. Remember you'll have on average about 1:45 per question on the quant section, 1:30 on verbal. Try to identify which questions are meant to be difficult--for those, you'll occasionally need to allow 2:30 or even more--as long as you make it up with the easy questions.

Hope you find these general thoughts on timing to be helpful!