There seems to be an increased amount of spam activity happening on Facebook lately, and you may have noticed an increase in the amount of bogus friend requests you've received. As a general rule, if you don't know the person in real life, they shouldn't be a Facebook friend. There is a way to at least reduce the amount of requests by making an adjustment in Facebook's settings.
When you're signed into Facebook, click on the down arrow in the upper right corner of the page, and select settings. Then click on "Privacy," and this will take you to the Privacy Settings and Tools page. You could also click on the little padlock icon, and click "See More Settings" to get there. Here you can specify who will see your future posts, limit the audience of posts you've already shared, and more. The section we're going to focus on here is the "Who can contact me?" settings. There is a question of who can send you friend requests, and it's strongly suggested that you change it to "Friends of Friends." This should take care of a lot of those spam requests. There are more settings about who can look you up, whose messages you want filtered in your inbox, and more.