A toothpick's no good for painting anything - the tip isn't flexible, it won't fit into small crevices, the paint won't flow off of it properly, and a semi-decent brush will come to a much finer, more controllable tip. If you try to blackline your figure using a toothpick, all you'll do is mar the existing paint job with big, crude black streaks (he says, fondly remembering the old TSR minis that he ruined thusly long ago). No, it's down to a smaller brush and a little practice. Games Workshop sells a good starter set that comes with (from smallest to largest) a detail brush, a standard brush, and a brush for drybrushing. Other company's sell pre-packaged sets as well, but I'd guess the GW set is most likely to be at your FLGS's shelf. Make sure that you thin the black paint a little on a pallet, and it should go pretty much where you want it to.
For drybrushing, you get some paint on your brush, and then brush it onto a rag or paper towel until there appears to be no paint left. Then, using light, quick strokes, brush back and forth over the area to be highlighted. A good way to practice this is to paint an old miniature entirely black. Then, drybrush white over the top of it. This'll let you get a feel for how much paint you need and how lightly you need to brush it on. I recommend having a brush just for this purpose - a brush that's on drybrush duty soon becomes unsuitable for anything else as the tip curls and frays from the rough treatment. Also, when removing paint from the brush or applying paint, use brushing motions rather than "splotching" - splotching will kill the bristles even faster than drybrushing will. Hope this helps!
