thank you for asking this!
if it’s a family/friend at home, try and make sure they’re in a bed/couch. if that’s not possible, try and move them to a carpeted area and put a pillow under their head. loosen any tight clothing around their neck.
if it’s in a public place, gently guide them to the ground, try to use a soft purse or jacket to place under there head. loosen any tight clothing around their neck.
roll them on their side, but if they’re already having a seizure when you get there, DO NOT try and roll them on their side.
make sure there is nothing in their mouth, and don’t put anything in their mouth. and please, for the love of god, do not try and hold them down to stop the seizing. this could result in serious injuries (why i’m in the hospital now).
there isn’t much else you can do. try and see how long the seizure lasts (even though it can be scary to watch a seizure). a typical seizure lasts from 60-90 seconds. if it lasts more than 3 minutes, call 911 immediately.
after the seizure is over, DO NOT leave them alone. they will be very confused and disoriented. try asking them some simple questions like “what’s your name?” “what’s you birthday?”.
also, if you were unable to before, turn them on their side now.
if they’re conscious, ask them if it was their first seizure. if it was, call 911. if they are bleeding from their head, call 911. if they tell you they want to go to the hospital, call 911. if they aren’t responding after 4-5 minutes, call 911.
other than that, there isn’t a need to call an ambulance. most people with epilepsy have been through this before, and will just be sore and weak after their seizures (though this varies for the types if seizures)