Blood pellets are among the most popular methods adopted by actors to give a realistic touch to scenes that involve blood. In addition to coming in handy for the performing arts, blood pellets also work great for Halloween. These are basically gel capsules filled with fake, non-toxic blood that can be tucked away in the desired location, and punctured whenever you need to create the effect of bleeding. These are easily available at most costume supply stores, and can also be ordered from a theatre supply company. Blood pellets are also fairly easy to make on your own (purchase empty gel capsules from a drugstore, and fill them with a nontoxic red liquid).
Blood stickers are yet another option for those who are looking to painlessly create the effect of bleeding. These are stickers shaped like bleeding wounds that can be applied to the skin in the desired spot. Most Halloween supply stores will carry these, and the only thing you need to keep in mind in this case is that the sticker should look as realistic as possible.
If you do not have access to blood pellets or blood stickers, you can take the DIY route, and fill thin, delicate plastic bags with red liquids like ketchup or non-toxic paint. The actor/actress can tuck these into their clothing, and discretely puncture them on cue to create the effect of blood.
Cover weapons with fake blood
If you are unable to pull off the fake blood act, another painless way to make a character appear to bleed is to cover the weapons being used against him/her with fake blood. If you happen to be using knives, or swords, etc, you can simply have the victim turn his/her back to the audience, pretend to thrust the weapon into the actor/actress, and discretely cover it with blood before you draw it back out to show the audience.