Photoshop behaving strangely?
Reset Photoshop to defaults
PC: Edit > Preferences > General - Reset Preferences on quit
MAC: Photoshop Menu > Preferences > General - Reset Preferences on quit
This resets all the settings when you quit - on opening settings are reset

How do you add or subtract from a selection?
To add to any selection with any selection tool hold down shift and select or draw around area to include.
To drop off from any selection with any selection tool hold down alt and select or draw around area to exclude.

Can you save a selection to use later?
Once a selection has been made you can save that selection for future use -
Select Menu > Save Selection - save to a channel which can be used to make the selection again as long as you save the file to include channels i.e. a .psd

How can you paint a selection with a paint brush?
Quick Mask
This allow you to switch between standard mode (know as marching ants) and painting mode. Painting black hides/white reveals.
Quick mask mode is at the bottom of the tool box and can be short cute using the Q key on the keyboard -  switches between the two modes

How do you selecting hair or fine edges?
Make a rough selection using the quick selection tool… then select:
select and mask button in options bar - use refine edge tool to define fine detail…
Use paint brush to paint directly to the mask - Painting black hides/white reveals.

How do you make a non-destructive change to a layer?
With a layer selected and an adjustment layer to make non destructive changes to a layer
To apply the changes just ti the pixel data on a selected layer create a clipping mask

How do I apply only to pixel data on one layer?
Either select use previous layer to create clipping mask in the new adjustment layer dialogue box off hover between later - holding down alt key and clicking to create or release a mask.

How can you hide pixel data non-destructive on a layer?
use masks to hide or reveal pixel data on a standard layer or to hide or reveal changes made with an adjustment layer.
When working with layer masks - painting black hides - painting white reveals - for both pixel data and for properties applied via an adjustment layer

Can not paint to a layer?
You can not paint to the pixels on a smart object - it must be rasterised (turned into pixel data) before you can paint to the layer

How do I protect pixel data on a layer?
Convert to a Smart Objects
Smart objects protect the pixel data in a layer. you can scale rotate a smart object with out any loss of the original data
Any placed file in Photoshop becomes a smart object - you cannot edit the pixels.

How can I apply filters non-destructive on a layer?
Convert to Smart Filter
Photoshop filters are destructive by nature - editing pixels directly - to use smart filters non-destructively
turn a pixel based layer into a smart object, Select convert for Smart Filter in the Filter menu - any filters you use will be non-destructive and editable

How do I set my colour setting across the creative Cloud applications?
Use Abode Bridge
To sync your colour settings across your creative cloud applications - apply through Adobe bridge - Edit > colour settings