Taken from Aaron Blaise, who has a nice demo of this on YouTube that does some neat foliage work.
This works with any image you want, just make sure the background is transparent.
Settings:
Set Control Panel > Load Brush After Each Stroke to On
Set Control Panel > Clean Brush After Each Stroke to OffIn general: Don't use extreme values for settigs. Keep the values low, especially for Jitter
My YouTube Photoshop Brushes playlist
Marco Bucci's 10 Minutes to Better Painting Series
(Above) Sinix Design - The Best Brush for Digital Painting ( on YouTube) Worth watching together. I don't entirely agree with him, but he does have a good approach. I like working with small brushes and don't mind the 'color pencil' effect he complains about.
If you have a few brushes you use a lot, it's a good idea to organize them into a separate folder in the Brushes panel. But if you drag a brush from one brush folder to another, there is no 'Duplicate' or 'Copy' brush option, so you have to select the brush you want, click on the + button, name it appropriately, then move the new brush into your brush folder. Silly, it should just be option-drag. What you don't want to have happen is to move a brush from a collection to a personal folder without copying the original first.