Working in Photoshop can take a lot of extra time if you have to look through lots of menus to find what you want. Using keyboard shortcuts not only saves you time but also makes using Photoshop so much easier!
These are some of my favourites and the ones I use the most:
M Marquee Tool
F Fullscreen (Press again to switch between modes)
X Switch between background and foreground colour
[ or ] to increase or decrease brush size
Hold space bar down for the hand tool
Ctrl – Shift – N Create new layer
There are of course many more but these are the ones I use every time I open Photoshop.