Krylon flat camuflage costs about four dollars a can at Walmart. Just take a paper towel and tear some jagged strips. -Even that is not necessary if you practice a little. Go from the lightest colors to the darkest. Use green, tan, sand, and dark green or black.
Easy to do and looks good
Chip
I do not recommend using black. From the several paintchemes I've had, the ones with black stood out the most.
For AZ, I've found that Tan, Brown, and Green works very well. I always use Krylon Camoflauge colors, straight from the can.
Some items I've used for masking:
-masking tape
-torn paper
-leaves
-forest floor debris (like pine needles, twigs, etc)
-paper bits from a shredder (my favorite! Paint the lightest color, let dry. Wet the bits to form clumps and place on dried paint and spray over with darker color, removing clumps immediately. Repeat for ever subsequent color) VERY effective.
Most of my paintjobs, however, were simply done freehand.
The best piece of advice I can think of is to not overthink it! When you do this, you will surely ruin your blaster. Also, stop before you think you're finished. Give it a day, and add to it if you see fit. Painted weapons are easily overdone.