By default, Photoshop retains several things in memory–undos, items you’ve copied to the Clipboard, a documents action history, and defined patterns. These items can be an enormous drain of memory and are usually the source of low memory errors. Therefore, purge these items from memory as often as possible. To do so, choose Edit, Purge, All.
Photoshop Tips
In the Layers palette, when you choose Duplicate Layer, you can change the document setting to “New” to create a brand new picture from any layer. I wish I knew about this one a few years ago!
Some filters, such as the Render filters, are disabled in CMYK. To get
around this, work in RGB mode with CMYK preview turned on (CTRL/CMD+Y).
Build your file as normal; when you are finished, convert it to CMYK.
This will allow all the filters to work, give you a smaller file, and
you won’t lose your colors when you convert the file. Only use CMYK for going to a commercial printing press.
You’ve got a zillion Photoshop windows open, and now you want them all to go away. How long would it take you to close them manually? No need — just hold down the shift key when you go File> Close and Photoshop will close all the open documents.