1. Make sure you have a recent backup
Make sure you have a recent Time Machine backup on the machine you wish to transfer your information from. To check, go to System Preferences (Apple menu) > Time Machine. If you see a recent backup, then you're set; if not, click "show Time Machine status in the menu bar." In the resulting menu bar item, click "Back up now." Time Machine will make a new backup.
2. Make sure you're not leaving anything behind
In the Time Machine System Preference pane, click the Options button. In the dialog box, you can see all the folders you have chosen not to backup -- check these to make sure you really don't want them. If you do, click the folder and chose the "-" (minus button) at the bottom. Click OK and backtrack to step 1 to create a current backup.
3. Getting the new machine ready
From this point, you can deviate into two directions:
- If your Mac is new: Boot up the new Mac and go through the setup screens. When the setup assistant asks if you want to migrate information from your old Mac, choose "From Time Machine backup or other disk."
- If your Mac has an existing account, don't fret. Just open "Migration Assistant" located in /Applications/Utilities.
Once you have completed the above step, click continue. Migration Assistant will ask you to specify the backup you would like to transfer to the new machine.
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5. Select the account you wish to transfer
You will now be presented with a dialog showing all the accounts that were on the old machine. Select one, two, or all of them, and click continue. If you want more options (such as what to transfer), click the gray disclosure triangle next to the account name. The resulting view will allow you to opt-out of transferring certain folders (i.e. Pictures, Documents, etc.).
6. And you're done ... almost
In the next few dialog boxes, you can opt to transfer Applications or Network Settings. Once you click transfer, your account will be copied in its entirety to your new Mac.
An important note: If you already have an account on the Mac you're transferring to, the account name cannot be the same as the one you're transferring. In other words, you can't copy an account if one exists on the new computer with the same name.