FarmVille is on a social networking site so it only makes sense that players would be rewarded for social networking in the game.
Getting neighbors is probably the best way to level up in FarmVille.
While it may be the best it may not be the easiest so here are some tips on where to find friends to become your neighbor.
Close Friends: Ask your close friends on your Facebook.
Most would not mind joining FarmVille and becoming your neighbor at all.
Friend's Friends: If you know any of your friend's friends or have recently added them then why not just ask then.
Tell them how exciting and fun the game is or you can see if they have any interest in the game already.
Forums: Using forums is a great way to get neighbors but if you go to a forum that is about FarmVille most it will be saturated with people trying to do the same thing as you so pick your forums wisely.
YouTube: Comment on videos or find channels with people that play FarmVille and try to get them to become your neighbor.
There are many ways to gain more neighbors but a lot of these ways are kept secret by higher up more experienced players.
Adding friends, your friend's friends, going onto forums and looking for people and using YouTube or other social networking type sites are good basic ways for people to get more friends which means more neighbors which means more cash for you!