There are few things that are known that will cause the client to crash, for example the most common crash is involved with casting spell rapidly, the system only allow 3 cast of spell in 1 second, if you are trying more than that if you are not lucky the system can't keep up with the routine and will consider you as a bad packet that need to be dropped, thus will cause your client forcefully disconnected.

The same rules applied to other action, such as attack, pick up, emoticon and any other action that is faster than allowed by the system may cause your client to crash.

Beside that the slow connection also may caused the client to crash, if your client can't keep up with the system routine, you will most likely get disconnected automatically by the system.

So if you crashed often you may need to check guide buletin #137, if it is applied then you may need to check your delay when doing any action especially if you are doing it with macro helper, and lastly check your connection to server

Thank you