How do I move my spawn point?
Solution 1:
In Minecraft Beta 1.4 and later, sleeping in a bed will set your spawn point.
On older SMP servers running Minecraft Beta 1.3, spawn points can be changed using the /setspawn command, provided the server is running any of the common mods to provide this functionality. Sometimes this command is called /sethome, and sometimes the /sethome command has a different purpose.
There is no way to set the spawn point ingame on Single Player Minecraft Alpha/Beta < 1.4. Some third party tools will change it for you however.
For Minecraft Classic, pressing Enter sets the spawn point.
Solution 2:
Simply make a bed and lay into it. If you're in multiplayer mode, you don't need to wait for all others to also get in a bed in order to sleep - laying down is enough to change your spawn point so long as your bed doesn't get destroyed.
Solution 3:
You can't do this without cheating.
If you're okay with cheating, you can use NBTEdit using this guide.
Solution 4:
The location of the spawn point can be changed if the player digs 3 spaces downwards from it. This will however only move the spawn point a few blocks away from the original location; it is not possible, using this method, to dramatically or controllably alter the location of the spawn point but there is tools that allows you to change the spawn point.
From http://www.minecraftwiki.net/wiki/Spawn