If you find a message that is wrongly classified as spam, select the message and click the Not Spam button. Unmarking a message will automatically move it to your inbox. This also applies if you are using web based email only.
If you are using client based email only then you have to make sure to check your web based email and check your spam folder and select which email you mark it as Not Spam.
Best thing you could possibly do if you find that some senders' messages are consistently being mislabeled as spam, you can prevent this by adding their email addresses
to your Contacts list (Whitelist).