First of all, it's not a competition to see who has the most friends. It doesn't matter if one person has 500 "friends" and you have 10 friends, but they are really close friends.
Secondly, don't feel like you have to accept all your friend requests. Sometimes you don't feel like being friends with someone. It's okay.
Thirdly, don't add everyone just to get rewards. It's really not worth it.
Fourthly, if you don't know how to add someone, click the green button that says "Add" with a plus sign by the user's name, gender, etc. If you want to delete someone as a friend, click the red button that says "Delete" with a minus sign. It should be in the spot that the "Add" button used to be.
Fifthly, don't ask everyone to add you. It's not worth it, and it makes some people NOT want to add you!
Hope this helps!