Before attempting CPR on a patient there are several things you must do. Make sure you and/or the patient aren’t in any danger—if possible, resolve the danger and if not, move the patient out of harms way. If unable to, for whatever reason, immediately call 911.
Check the patient and see if he/she is conscious or not. Do not check for a pulse because time is of the essence and finding a pulse can take too much time. Call out to the patient asking, “Are you okay?” Repeat if necessary, and if the patient doesn't respond, immediately call 911 and then perform CPR—initiating Circulation, Airway and Breathing Tasks (the C-A-B’s) and not the A-B-C’s. Also, if possible have someone else call 911 and begin CPR, immediately.
It's important to note: that the AHA guidelines recommends in-confident performers should, at least, perform chest compressions upon the patient, since studies show chest compressions can be as effective as the combination of CPR.