Ask questions that are pertinent to their current complaint. Especially if it's cardiac, you want to know as many details and associated symptoms as you can. Also consider things that your receiving facility might want to know. Details such as height/weight, do you smoke, etc etc save the nurse a little time during their triage. (Also as a bonus, asking them their weight is a good way to practice doing lb to kg conversion and calculating weight based med dosages).
If you've asked everything you can think of, and you still have a few minutes left before you hit the ER, try and make small talk! This is easier said than done for some people, but it honestly can put sick people at ease, and distract them from their current condition a little bit. Also always do your best to reassure them and let them know they will be well taken care of.
It all takes practice and a certain comfort level, but after awhile and enough interactions with people it will feel like second nature!