You know that expression you're mixing your metaphors? For a long time, I didn't know what it meant. It's totally okay if you don't know what it means, either, because I made it a point to figure it out...and now I do.
Mixing It Up
By its very definition, a metaphor is a little ambiguous. Basically, it's a figure of speech. Metaphors do not make literal sense. For example, writing love is a rose in full blossom is a metaphor. When you say learning is a journey, it's a metaphor. To apply a word or phrase to something that doesn't really fit is to create a metaphor.
So what the heck does it mean when you mix metaphors? You've heard the phrase we have to tighten our belts. It means that you're going to be cutting back on expenses to save money. You've also heard the phrase empty pockets. Even if your pockets aren't literally empty, this metaphor means they're empty of money. So if I were to say we have to tighten our belts because our pockets are empty, I'm mixing metaphors. It comes across as being nonsensical when you mix metaphors like this. Other examples are even more comical:
I smell something rotten here, and we have to nip it in the bud.
If we cut off our noses to spite our faces, we won't have a clear avenue of escape.
It's sink or swim. You'll either stand on your own or you won't.
The three mixed metaphors above just don't work. In the first example, we go from smelling something foul to cutting something off. You can't nip a smell, so it just comes across as silliness. In the second mixed metaphor, everything is tangled. First you're bringing up an image of noseless faces, and now we're suddenly scrambling along paths with no end in sight. Why? And the third example is the most ridiculous. Are we swimming or sinking or standing or what?
Mixed metaphors are unclear, and sometimes they end up reading as pure nonsense. Unless you're writing Mother Goose-style or Dr. Seuss-inspired books, I suggest you shy away from mixing metaphors. A single metaphor per sentence is more than enough. When you try to use two metaphors in the same thought, you're going to get in trouble.
So look over your writing, look at your metaphors...and eliminate the ones you don't really need. Metaphors are best when used in moderation.