what are the different priorities to consider in doing first aid

Depends on the situation. I am going to quote Maslow is heirachy a bit while I go through first aid a bit:
1. oxygen - so u will note that the airway is clear
2. fluids - ensure that all bleeding is secure, ensure that bleeding is stopped; ensure that u r doing ur best to be STERILE if u can while stopping the bleeding
3. Next, if there r any bones broken, u want to do ur best to stabilize them - & if any r sticking out of the skin - of course be STERILE with them as well. Even if it means placing a clean towel over them. The very best way is to soak the clean towel in sterile water/saline & then apply it to the area.
4. In the even of a seizure/convulsion, place the patient on the floor & and turn them on their side. Remove anything obstructive from their neck. That is it. Do not stick anything in the patient is mouth.
5. Last, if the patient gives the ''universal sign'' of choking - hands clasped around throat - perform the Heimlich maneuver until the food becomes dislodged. This may take a few times.
Basically u will take care of oxygen first, then fluids, then whatever else is going wrong. That is the order in which it goes. Hope that helps.

A .B. C . and the differance between adult and child first aid..application..severity in bleeding and the life threatning conditions present..is it life threatning? Time avaiable to solve problem..{hospital location} ... Enviorment surrounding situation of patient.and incident.. can patient communicate?

Danger- to yourself & to the casualty. If by assisting u r placing yourself (or others) in danger, then u will not be assisting!
Response- r they conscious
Airways- r the airways clear
Breathing- r they breathing
Circulation- r they bleeding? do they have a pulse?
Defib- early defibrilation will be of most benefit if the heart has stopped for any reason

If there is more than one casualty, u need to assess who needs help first. generally a noisy person is fine, but an unconscious person can stop breathing. First priority is someone who is not breathing, then heavy bleeding or shock. If someone can yell & scream, chances r good that they're able to help themselves to some degree

First - Never endanger yourself. Do not stand in traffic, in a burning building, go near a downed power line, or touch another is blood if you can avoid it.

Second - Treat the most life-threatening injury first. Bleeding needs to be controlled, yes, but if the patient is not breathing, you're not helping much.

Is this what you're looking for?

Is there a heartbeat? Is the patient breathing? Excessive bleeding? If no to first question do CPR. If yes to the third question, apply bandage and pressure.

A.B.C.
airway breathing circulation

airways open not blocked breathin shallow laboured or normal cirulation normal or irregular

Stop bleeding and secure breathing first