If you subscribe to my newsletter, then you'll remember that last month I mentioned being mindful of different spellings of words depending on how they are being used. Yes, I'm talking about the same word being spelled differently if it's used as a noun, verb, adjective, etc. Crazy, right? That's the English language for you. ;)
Grammar geeks like me thrive on this stuff, but the typical writer does not. My suggestion is to make Merriam-Webster and Chicago Manual of Style your best friends. I always have a tab open to Merriam-Webster to make sure I'm using the proper spelling for words. I also refer to Chicago manual of Style's hyphenation table quite frequently. As an editor, I have to do this because I don't want errors in my clients' books. But all authors should do this. Here's an example of what I mean:
speed dial — This is the noun form. I hit four on my speed dial.
speed-dial — This is the verb form. I speed-dial Trish.
Spell check (Ugh, don't get me started on spell check!) won't catch these mistakes. (Spell check is stupid. It often suggests changes that are incorrect! Oops, there I go again.)
So, if you're unsure of a word—whether to hyphenate it, write it as one word, or write it as two—check Merriam-Webster and Chicago Manual of Style. (Seriously, bookmark both of those pages!) Your editor will love you for it. ;)