Hi Sue!
I get bleed too, so I do my best to avoid black lines.
Stamp_A_Licious was having trouble too, and she found that stamping with Ancient Page coal black ink doesn't cause her any bleed trouble. Other people have found that using a different brand of mineral spirits works better for them. MamaKimberly found that for her, Gamsol brand works best.
I don't think you're doing anything "wrong".
I use the following products:
Prismacolor Artist Pencils
Koh-I-Noor Woodless Progresso Pencils
Pre-Tested Odorless Mineral Spirits by Grumbacher (but have used Gamsol, Natural Turpenoid and one other brand that I'm not remembering the name of with just as good results)
Stumps and Tortillions from DickBlick.com
Black Stazon (99% of all of my images are stamped with Black Stazon)
Whisper White or Very Vanilla paper
Maybe others will have suggestions for you too, but that's my .02.