When referring to the keyboard, use maximal capitalisation for the key names:
Ctrl Alt Shift Home Print Screen F5 Space Backspace Page Down M
Do not write the key names in quotation marks or enclose them in angle brackets.
Caution. Not all keyboards have the same keys, and new keys are added from time to time. Avoid referring to media keys (eg volume up and down), computer control keys (eg screen brightness) and specialised keys (eg to launch search or a mail program) unless sure that readers have the same keys.
Also take care when writing for international audiences, because keyboards for different countries are not the same. For example, the United Kingdom keyboard includes a pound sterling sign (£) and has some other symbols in different positions, compared with the United States keyboard, which is used in Australia.
Some keys are labelled differently from keyboard to keyboard:
PgDn or Page Down PrtScn or PrtSc or Print Screen Ins or Insert Del or Delete
If necessary, define the key name the first time it is used:
Press the Menu key; it is usually found immediately left of the right Control key and may look something like this: ▤.
Use the names even when keys are also known by a symbol, because symbols can change from keyboard to keyboard and version to version:
Windows Key rather than 
Command rather than 
The Space key usually does not have a label, but because Backspace uses a capital, it is consistent for Space to use a capital. Capitalisation is also useful because space is a relatively common word.
Insert a space by pressing Space.
