When administering first aid. what is your first consideration is?

The very first thoughts going through your mind should be, "is the scene safe to enter?", and "do I have my body substance isolation?" (BSI). Make sure you're safe first, because you won't be any good to the patient/victim if you get yourself hurt. Following that is your initial assessment followed by ABC's (airway, breathing, circulation). After that comes whatever treatment is necessary for the specific injury or illness.