startup disc full
I don't know how to best empty or move files away from start up disc to stop getting this warning
Go step by step and check.
1. Start up in Safe Mode.
http://support.apple.com/kb/PH11212
2. Backup your computer.
3. Empty Trash.
http://support.apple.com/kb/PH13806
4. Disk space / Time Machine / Local Snapshots
Local backups
http://support.apple.com/kb/ht4878
5. Delete old iOS Devices Backup.
iTunes > Preferences > Devices
Highlight the old Backups , press “Delete Backup” and then “OK”.
http://support.apple.com/kb/HT4946?viewlocale=en_US&locale=en_US
6. Re-index Macintosh HD.
This will take a while. Wait until it is finished.
System Preferences > Spotlight > Privacy
http://support.apple.com/kb/ht2409
7.Try OmniDiskSweeper. This will show the storage size details of the items.
https://www.omnigroup.com/more
Select Macintosh HD and click “Sweep Selected Drive” at the bottom.
Be careful. Delete only the files that can be safely deleted. If you are not sure about any file, don’t touch it.
8. Move iTunes, iPhoto and iMovie media folders to an external drive.
iTunes
http://support.apple.com/en-us/HT201562
iPhoto
http://support.apple.com/kb/PH2506
iMovie