Working a trick (spell), fixing a hand (creating a mojo bag) or any number of other workings are usually done with ingredients referred to as "personal concerns." These are things associated with the person the work is intended to effect.
In some ways, personal concerns help the work you're doing understand who they're supposed to effect. It isn't enough in hoodoo to just concentrate on who you want it to effect - if you do your magic right, the magic keeps "cooking" long after you've stopped concentrating on it, and if you don't tell it who to effect, it'll sit there and do a whole lot of something to no one at all.
Some personal concerns are more powerful than others. They're more "personal," as it were - they give a better "lock" on the intended target of that work. In her book Hoodoo Herb and Root Magic, author cat yronwode talks about the personal concerns in descending order of power. Within each category, there is also a "better than" list, as well, which is listed below. It looks something like this:
- Sexual Effluvia: Combined sexual fluids, semen, vaginal fluid, menstrual blood.
- "Private" Biological Effluvia: Urine, feces, bath water
- Hairs: Pubic hair, body hair, armpit hair, beard hair, head hair
- Unwashed (Soiled) "Private" Clothing: Night-clothes, socks, stockings, underwear
- Measures: Genital organ measure, other body part measures (waist, wrist)
- Foot Tracks: Foot skin scrapings, toenails, foot track dirt, shoes, foot-wash water
- "Public" Biological Excreta: Sweat, spit (saliva), hand-wash water, fingernails, saved baby teeth
- Unwashed (Soiled) "Public" Clothing: Hat sweat band, hat bow, hair ribbon, handkerchief
- Pictures and Images: Photograph, drawing, silhouette
- Personal Mementos: Person's handwriting, something person once owned
- Impersonal Mementos: Person's business card, news article or ad mentioning person's name
- Name-Papers: Person's full name written on paper by you, person's birthdate
Generally speaking, it can be seen that the more private and personal the concern, the more power it has to affect that person. In essence, the more you can "get in his business," making off with something the person keeps to him/herself, not making public, the better it will work.
Some concerns are traditionally associated with certain kinds of magic. Sexual Effluvia was almost always used in love magic, while Foot Tracks are the preferred concerns of controlling magic.
If a specific working mentions a specific kind of concern, it is best to use that - it's there for a reason, even if it's just the weight of tradition. If it mentions just having some kind of personal concern, then the higher up this list the concern is, the better it will work. If it mentions nothing, then feel free to use any of these - in general, though, you should always incorporate a personal concern of some kind, even on magic you work for yourself.
Remember, a working is like a train, and the personal concern is like the tracks: without it, it may be running at full power, but it has no direction to go.