Use one space after the full stop at the end of sentences. And no spaces either side of forward slashes.
√ Either/or
x Either / or
Use UK English rather than US English unless you’re writing for a US audience only. When in doubt, refer to an established British English dictionary (for example, the Oxford English Dictionary).
√ Optimise
√ Behaviour
√ Travelling
x Optimize
x Behavior
x Traveling
Where a word can be spelt using either one or two of a particular letter, then use one.
√ Focused
x Focussed
√ Targeted
x Targetted