Lindsay--With just 4 nights you won't see much of the ring road highlights, but you do have time to really see some great areas. I would do the first night in Reykjavik to get over jet lag and see the city. If you are up for a lot of driving, you could do the Snaefellsness Peninsula, Reykjavik and some of the south coast. Or you could do Reykjavik and the south coast and not be as rushed, which is what I would suggest.
If you did that, I would stay in Reykjavik the first night to get over jet lag and to see the city. Then in the morning I would head up the south coast towards Vik. That is only a 3 hour drive, but there are so many stops along here that it will take longer. Or if you can go a bit further to Hof, that will be about 5 hours drive time. If you did that though, you could do the zodiac boat tour at Jokulsarlon the next morning as well as Diamond Beach and then meander back down the south coast and stay the third night somewhere around Vik. The next day I would meander back down the south coast to the vicinity of Hella or Selfoss. Then you could do the Golden Circle as well. Without knowing what time the last day your flight is, you might even be able to do some of the Reykjanes Peninsula. The problem is there are SO many options and SO many things to see, so it gets hard to narrow it down. We have been a handful of times and still succumb to this and try to cram too much stuff in;)