I picked a new vase (read about when I found it here) that was half as tall and significantly wider.
I always put in the leaves first
Cut off all the flowers that are droopy or broken, you can tell the ones that are just not going to make it.
Then cut at a variety of sizes, add a little 7up to the water to keep them going strong. I learned this from the movie Bed of Roses. I love that movie, If you have not seen it you should check it out. I am going to have to watch it again soon.