Blood magick isn't recommended for beginners - ever. Its very powerful. Not dangerous or bad if done correctly, but one must understand all the basics of magick first to be on the safe side.
When doing any blood magick, it creates a stronger link between witch and spell. But if you aren't sure how to focus this, it can be a bad idea. And purposely making any major cuts in an attempt can be harmful because of infection, weakening your aura from too much blood loss, and such. So it can be a health issue too. Though an alternative for women is to use menstrual cycle blood so not to cause any physical harm to themselves. I've read in books and articles that smearing this naturally released blood on tools was a common way to link the tool more personally to a female witch. But I've never known anyone to actually do it. But it is an idea.