You won't know which section is experimental. You will know which type of section it is, though, since there will be an extra one of that type. Knowing that the experimental section can be disproportionately difficult, if you do poorly on a particular section you can take some solace in the hope that it may have been the experimental section. In other words, do not allow one difficult section to discourage your performance on the rest of the test. Although time is strictly limited on the GRE, working too quickly can damage your score.
Many problems hinge on subtle points, and most require careful reading of the setup.
Because undergraduate school puts such heavy reading loads on students, many will follow their academic conditioning and read the questions quickly, looking only for the gist of what the question is asking. Once they have found it, they mark their answer and move on, confident they have answered it correctly. Later, many are startled to discover that they missed questions because they either misread the problems or overlooked subtle points. To do well in your undergraduate classes, you had to attempt to solve every, or nearly every, problem on a test. In fact, if you try to solve every problem on this test you will probably decimate your score.