Is your search box clearly visible and quickly noticeable?
Let your shoppers hunt for products, not for your search box. Make your search box stand out so that people can easily find it.
Avoid using only a submit button without the text field. That will make the search box hard to find. Also avoid having only the text field without the submit button, not every user knows that they can hit enter to submit.
Placement of the search box:
Position your search box away from all other boxes such as email signup. Place it consistently on all pages except the checkout page. Top right, top center or in the main menu are popular positions for the search box.
Size of the text field:
Along with making the search box more prominent, a longer search field will also allow the users see what they type which would reduce errors. Make sure it can hold at least 30 characters. Another thing you could do is to look at your Site search data, find out what your shoppers are searching for and use that to decide what the optimal character limit should be.
Make sure, the color of the input field doesn’t make it hard to understand where the search term should be typed in. Increase the contrast between the site header, text field and search button to increase the prominence of the search box relative to other elements.