Some possible safety improvements:
1. New cars. This was already set to happen; the new cars have shielded rear wheels, which should make them safer.
2. Don't race on the wrong kind of ovals. As Dario said, Las Vegas is very steeply banked, allowing Indy cars to travel around it way too fast. Ovals like that should be for stock cars only. Pack racing is also dangerous; the most suitable ovals prevent the Indy cars from racing 3 or 4 abreast. Part of the problem with Las Vegas, as Jody Scheckter pointed out, is that it's so easy to stay flat around it that even the worst drivers are as fast as anybody - apart from the track design, that also facilitates dangerous pack racing.
3. Install ballistic plexiglass on the catch fencing. This should prevent cars from being torn up if they miss the top of the safety wall when they crash.
4. Don't have large numbers of cars racing on the shorter ovals (34 cars at the Indy 500 isn't so bad).
5. Scrap double file restarts on the road courses. These were intended to improve the show, but they tend to lead to cycles of repetitive crash - restart - crash - restart - crash. This both causes needless crashes, and seems farcical.
6. Improve driving standards. A tough one obviously - but all of the oval races have seen reckless wheel-to-wheel racing. Some of the drivers clearly aren't up to scratch (at least Milka Duno is no longer "competing"). Overtaking attempts on road courses regularly lead to crashes (admittedly, this is partly because the road courses and the cars generally do not facilitate overtaking).
Jimmie Johnson has suggested that the Indycar series stick to road courses in future. However, this is one safety improvement I cannot countenance. The series might as well disband, rather than do that. It's based around the Indy 500 after all! Besides, most of the road course races in Indycar are processional; safety problems aside, the oval races are vastly better.