Hands up if you’re sometimes unsure about when to use a hyphen. I know I was before I studied editing.
Here’s a tip: a hyphen removes ambiguity.
two monthly payments
The first could mean either two payments a month, or a payment every two months. The second is very clear.
The words two and monthly are working together to describe the payments. The hyphen shows this. It’s joining the words to make a compound adjective.
Where it can get confusing is when a pair of words is sometimes hyphenated and sometimes not.
The trick is to think about whether the pair of words is describing something (compound adjective)
I provide self-editing tips.
or is simply a thing (compound noun)
I provide tips for self editing.
It’s not a hard and fast rule, there are compound nouns that use hyphens (decision-making, daughter-in-law, two-year-old) but it’s a handy test. If the phrase is clear without the hyphen, then you don’t need it. Especially given the fashion is moving towards less punctuation.
Hope that helps.
If you want a bit more word-nerdery, you might be interested in this post about dangling modifiers (yes it’s a thing).
Or if you want to dig deeper into hyphenfry (I made that up) you can’t go past Grammar Girl. Here’s a podcast of hers on the subject