So if you do book signings etc make sure there is a nice big sign that has your FB address and more importantly why they should follow you i.e. keep up to date with my latest book releases and short stories follow me on FB etc I am assuming you regularly make updates to your FB page?!
Again if you do a signing stick a postcard with those details in each book you sign etc.
Any interviews online, tv or radio just throw it in to the conversation that people can find you on FB.
Hang out at libraries and tell people unless they follow you on FB you are going to follow them home... Then when you get arrested make sure it gets in the local papers.
Maybe don't do the last one unless you are already pretty famous, getting arrested seems to work for them quite often.