In reply to climbwhenready:
Put the mat down, think about where you're likely to fall if you come off the problem at different points, move the mat ...
Some problems are going to be iffy unless you have a spotter and/or a second mat (or, in some cases, three spotters and five mats). If you're going bouldering on your own, you have to develop your own judgement about what you're okay with trying and what you're not.
Grab a copy of the second edition of John Sherman's "Better Bouldering" (the second edition is massively expanded over the first one). The "Safety" chapter is gold and has tips on spotting, mat placement and so on which I've never seen elsewhere.
Have you bouldered indoors, or is it all new? If the latter, you need to learn how to land: aim to land with both feet evenly underneath you, bend your knees, and crumple backwards as needed. If the former, just be aware that portable mats tend to be harder than indoor ones -- they work, but it's not such a nice squishy landing (if your portable mat gets squishy, you may get hurt). And also that you don't want to crumple so enthusiastically that you crack your head on a rock behind you.
Be prepared for the mat to suddenly look a lot smaller than it did at ground level.