Though it is fairly unlikely that you will have to deal with a curse more than a handful of times in your magical practice, chances are that it will come up eventually.
If you are at all active within the occult or metaphysical community, it means interacting with people that do not necessarily have the same moral or ethical code as applied to spell casting.
Signs that you have been hexed:
The easiest form of curse to disarm are the obvious physical apparatus that require contact for activation. These include coins, mojo bags, herbs or even piles of dirt that are placed outside of your home. the latter two are the most likely suspects for "foot track" magic, in which the dirt that the target has walked through is used as a direct physical link, the same way that hair, fingernails, or blood are utilized. To disarm physical and obvious bits of spell craft, I strongly recommend having a bottle of rue oil on hand.
The essential oil is unavailable (as it is dangerously strong), but an infusion of the herb in olive oil (to disarm) or castor oil/mineral oil (to send the spell back to its originator, with a bit of nastiness thrown in for good measure) is much more effective anyway. Simply douse the item in rue oil. Do not touch it with your bare skin, and wait awhile before disposing of the object; in running water, a sewer, crossroads, or by burial away from your property. More advanced practitioners can use bits of hex craft to pack a whollop in "return to sender" spells, however, extreme focus, practice,appropriate shielding and purification are mandatory in this endeavor.
Less obvious signs of a curse are a sudden and completely unexplainable reversal of fortune. For example, in the course of a small amount of time, you lose your job, your lover suddenly calls it quits, your brand new car dies for no reason, and a million other little things relating to every aspect of life fall apart. Usually accompanied by a total lack of energy, fitful sleep, and nightmares (often of your tormentor).
If all health issues have been ruled out, and you have examined your actions for cause and effect, and you have done cleansing or purification to no avail, here is your best course of action.
1. Fill a large pan with Four Thieves Vinegar and set it in the bath tub.
2. Stand in the tub, naked, and with a clean (preferably new) white wash cloth wash your entire body with the Four Thieves Vinegar. Start at your head, work from the right side downward, the left side downward, from the heart to the hands (outward). Make sure to address the back, hands, soles of your feet, and hair.
3. Do not rinse or towel dry, but allow the mixture to stay on your skin fro 24 hours. Dispose of the leftover vinegar in a body of running water.
4. Do an appropriate protection spell and shielding charm. Naturally double terminated quartz are excellent for this.
5. By now, you should have at least some idea of "who dunnit". Confront them. More often than not, this is enough to scare them into stopping or convince them that you are bat shit crazy. They won't mess with you.
What comes next is entirely up to you. As Ghandi once said, "An eye for an eye makes the whole world blind", but don't present yourself as a weak target.