Previewing is in itself a very simple and obvious technique. Nevertheless, it is often forgotten, implemented only superficially or with a "guilty conscience". All too often we want to "just start reading right away" – or we are not very motivated and just browse through the text listlessly.
But previewing is an excellent way to motivate yourself to read! It doesn't take long, and you don't need to have high expectations for your comprehension. If you don't really feel like reading, set the stopwatch for just a few minutes – and then just do a casual, playful preview.
In the "ideal case", you find that the text is unimportant or that the information you get from the preview is already enough for you. Then you are done! However, if the text is important, the global preview information will help you with the subsequent reading: Individual details or difficult passages become more understandable if you can already embed them in a context. Thus your memory retention will be better as well.
It is advisable to look more closely at the first paragraph at the beginning of a preview – and then jump straight to the end of the text. “Spoiling" the results beforehand is just right for non-fiction texts! Only then flip through the text chronologically page by page. Often it is especially worthwhile to look at the beginnings of paragraphs (and of course at all contextual cues that are sticking out: titles, enumerations, italics, bold printing, info boxes, …).
Previewing helps you to gain an active, curious, questioning approach to the text. Always be guided by this basic “detective” attitude when reading! All too often we tend to work through a text in a bureaucratic way and just count the pages we still have in front of us...
Make a habit of previewing and be surprised how much more you can "get out" of it in terms of time gained or quicker understanding.