Basically, you would want to reduce a speed of Selenium WebDriver to make sure that your script does not fail as the element does not appear or takes time to appear. You can mostly do this by implementing Implicit Wait or Explicit wait.
Implicit Wait:
An implicit wait tells WebDriver to poll the DOM for a certain amount of time when trying to find an element or elements if they are not immediately available. The implicit wait is set for the life of the WebDriver object instance. driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
Explicit Wait:
It is more extendible in the means that you can set it up to wait for any condition you might like. Usually, you can use some of the prebuilt ExpectedConditions to wait for elements to become clickable, visible, invisible, etc
WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement element = wait.until(ExpectedConditions.elementToBeClickable(By.id("someid")));
Here you can wait for an element explicitly to appear or be clickable first then do an operation on it.
Say, you have a contact form which asks name and email address and when you click submit button, it simply submits the form and shows the thank you message. The submission happens through AJAX call, so you will know see whole page loading.
For such scenarios, you can use Explicit Wait to wait for the Thank you message to appear after you press/click submit button.
Hope that helps!