General First Aid Advice for Poisonings

Bites or Stings:

Wash the area with soap or disinfectant and water
Remove any stings or tentacles attached to the skin
For jellyfish stings, if there is pain, immerse the area in hot (but not burning) water for 15 minutes
Apply ice if there is swelling and cover with a sticking plaster

If the person develops an allergic reaction take them to a doctor immediately:
Rash, temperature, difficulty in breathing, swelling of the face and neck

See a doctor if signs of infection develop:
Redness, swelling, blistering, pain

DO NOT take an analgesic for pain without advice from a medical professional but it is ok to take an analgesic if stung by a common, non-venomous household creature.

DO NOT apply vinegar or methylated spirits to bites and stings
Vinegar is only effective for Box Jellyfish stings (an Australian Jellyfish)
Vinegar can make other bites and stings more painful

DO NOT apply ice to the hands or feet
This may cut off circulation