An echo happens when you use the same or similar word too close together. This is something you want to avoid doing whenever possible. When you are tempted to use the same word twice, think of ways to reword or restructure the surrounding sentences.
Example 1 (echo)
I surveyed the café, noticing that two strangers had sat down at one of the card tables along the painted mural wall. They did not seem like the type that frequented coffee houses, especially not a vintage cafe like this.
See the echo here. The word cafe is used twice in close proximity.
Example 2 (revised)
I surveyed the café, noticing two strange men sitting down at one of the card tables along the painted mural wall. They looked too clean cut, definitely not the type who would frequent a vintage place like this.
Sometimes a little reword does the trick.
Now, the biggest culprit of the infamous echo happens when we write what a character is doing.
In first person, it comes out I, I, I, I, I.
In third person, it comes out he/she, he/she, he/she.
It is so easy to fall into the, I or He/She trap. You're probably saying, "well, how the hell am I going to tell you he did something without saying he?" The trick is to reword and rework sentences to that you stretch out the gaps between words so that the reader doesn't hear it.
Let's look at some examples.
Example 1 -First person
I knew it was inadvisable to walk around the streets alone at night, but I did not have a car so I was forced to do it anyway. I carried my keychain of pepper spray, for defense, just in case I ran into anyone dangerous. I naively believed in its ability to protect me from any attacker.
Do you see all the I's? It's like an annoying drum beat after a while.
Example 2 - Revised First person
It was inadvisable to walk the streets alone at night. I knew this but didn't have a car, so there was no other choice. For defense, I carried a key chain of pepper spray, naively believing in its ability to protect me from any attacker.
Sometimes a little reworking helps to remove unnecessary I's.
Example 3 -Third Person
Sasha downed her drink. She winced as the liquid burned her throat. A warmth was building in her stomach. Two shots down in less than twenty minutes. She knew she needed to pace herself or this night wasn’t going to go very far. She knew Tequila was a dangerous alcohol. She'd heard stories of people doing crazy things when they drank a little too much of it. She made a quick mental note, not to have another drink for a while.
See all the she's?
Example 4 - Revised Third Person
Sasha downed her drink, wincing as the liquid burned the back of her throat. A warmth slowly built in her stomach. Two shots down in less than twenty minutes. Sasha knew she needed to pace herself or this night wouldn't go very far. Tequila was a dangerous alcohol. She'd heard stories of the crazy things people had done after drinking too much. Setting the glass down, she made a mental note not to have another drink for a while.
Mixing in her, with she, and the character's name helps to smooth out the echo. You will never completely avoid it, but by reworking the sentences you can make it a little less noticeable.