First of all, you need to determine the type of the sound you require, as it is best to know about it, in order to make your search faster and effective.
Look for the websites that offer huge quantity of sound effects. There are a number of public domain sound effect websites available on the internet. Yet, there are few of them that really provide a good variety.
Now look for the categories of your choice. The most common categories include machinery, natural, animals, computer and children. For instance, if you are looking for sound of a giggling child, then you can look it in children’s category.
Always try to keep your search organised, in order to find your desired sound in time. Many times it happens that people take too much time in search for the sound, and end up with just a matching sound, which is obviously not a good solution for the problem.
Whenever you finalise your sound, you should make sure that it is not copyrighted. Most of the websites clearly state that which sounds are royalty free and which ones are questionable. Therefore, it is important to cross check the copyrights, in order to avoid any legal action against you, if caught.
You should also read the fine prints, in order to check whether the sound is free to use or you need to pay for it. Therefore, you should always try to read website’s policy, so that you can get to know you are not breaking the law.
Once you make sure that the sound is free to download and is not copyrighted, you can download it and add it to your project.