How do I keep my ship alive long enough to kill the bad guys?

Someone told me that I should do the 'Epic Arc' that starts with Sister Alitura so I managed to find her but I'm stuck on the second mission. There are a couple of red ships and they get through my shield really quickly so that I have to run away, dock in a station, wait for my shield to repair and then try again.

How can I make my ship tougher so that I can finish of the NPCs without running away?

Edit: I'm using a Rifter