I mean, I cant lie...I've tried running a LS that was a failed experiment. It is just a balance on trying to find a core of people that you are friends with, and maybe bring in some of their friends. the attitude should be like I invite three friends, they invite three friends, etc...obviously this isnt gonna always work b/c people have commitments and established LSs, but i think that is the best hope. Throw in some random people and you can get a healthy mix of craziness, lameness, coolness, and fun
ZNMs are always fun, as is Pankration (love my Apkallu MNK). I'd like to also stress what everyone else has mentioned with alternating events. Usually it's Sky->Ein/Limbus/Kings->Dynamis->Gods->KS99, and some other stuff in between around King TOD and Wyrms. Spreading everything out is a good way to keep people entertained.
Strip-random!
I also agree with the smaller bullshit fun-run events. Eco-war, garrison, ballista, etc.
I've struggled with this myself as well. My shell right now has 25 registered members between our Dynamis/Ein Shell and our main HNM/Sea/Sky etc one. The only thing I can say is establish a good core group of dependable people. While my shell is small and thus lacks in claims for the most part, we do well for our size including our recent 11 man Ixion kill in 2h. The small events that encourage teamwork are good and beating each other up in Ballista is usually a good time too. Recruiting, I'm still searching for an answer there myself because I don't want to shout in Whitegate as said above ;/ I suppose building up the reputation of the shell should help there though if you can manage to do it.
Removing useless sack holders not only helps up the productivity of the shell, but lets the members know your are making sure that sack holder isnt just a popularity contest or status postion. Nothing I hate more then seeing shells that Sack older members just because they have been there a while. Time in a shell != Leadership ability.
Make good moves, get your members on board, and they will help recruit your shell for you.
i love me some ballista, gets the killer instinct juices pumpin!