English has a lot of words that sound the same when pronounced, but are both spelled differently and mean different things. These trickster words are homonyms and homophones and are the bane of many English teachers' existences.
Some quick definitions
Homonyms are words that sound the same, and may have the same or different spellings, as well as different meanings.
Homophones are words that sound the same, but are both spelled differently and have different meanings.
There are other types of words with varying levels of sameness (spelling, sound, meaning) but we'll just focus on the homonyms and homophones today. For the sake of ease, I'll just refer to these words as homonyms because that term refers to all words that sound similar, regardless of spelling and meaning.
Think first, then speak/write
Lots of us talk and write without giving much thought to the content of the message we are trying to convey. This is the first of many potential pitfalls of good communication. Thinking about what we mean to say, and then choosing words to most accurately convey that message can help us to Sound Smarter right from the start.
One aspect to choosing our words carefully is that we only choose to use words that we understand. Another technique is to use the simplest words possible. These two tips keep your message concise and clear.
If we're already thinking critically about our word choices, we are not likely to use the wrong homonym. It absolutely doesn't make sense to ask for a 'peace of cake' but 'piece of cake' does. If you're not sure, Google is your best friend. In most cases, a quick search of the phrase you're planning will bring up bevvy of results to point you in the right direction. Of course, this only helps if you are aware of the existence of multiple spellings. Here's a list of some commonly misused homonyms to keep in mind.