First, be sure to reboot your phone once in a while. Once a week at least. Just like your computer.
Next, it's always best if you keep it synched regularly and keep your firmware up to date. Some of us like me have an older phone and don't want iOS5 yet, but I may try it soon to let you know how it goes.
Keep your software up to date. Check the iTunes store periodically and keep your Haypi Kingdom app updates downloaded. Bug repairs are released from time to time.
Also, if you are using iOS4 or higher, and especially if you're on an older phone, you should try not to let too many apps run in the background. They eat up RAM memory that Haypi could be using instead! Without free RAM, it will crash when it gets too clogged up. So double tap home and then hit the minus to shut down things you're not using any longer to free up phone memory.
Last but not least, close down Haypi and release it from memory just like the above every once in a while. It will prevent untimely crashes. Do it yourself when the time is good, lol.
Keeping things closed out of memory has drastically improved my game performance! Hope some of this helps you too!