How do you start new legacies?

It's hard, but I've just  done this so I've been thinking about it. It isn't enough to have an open concept ("this will be my explorer Sim for new new pack) but if I am going to settle in, I have to produce a Sim I want to play - and CAS is not my strong suit. I don't depend entirely on the randomizer - but I do need its help to get started. 

For Enchanted by Nature, my initial  concept was to take inspiration from a TS3: Supernatural  household I had played for a few years - a Fairy/Werewolf odd couple. But I had recreated them already, without their occult life-states, not long after I migrated to TS4 and before this game had those. They wound up being my first TS4 legacy founders (in 3, they had never had children). But that whole save folder was lost with a dead laptop, and I had foolishly never saved them to my library or gallery. I tool a couple stabs at re-creating them but it never took off. 

The Fairy I ended up making is a TS4 re-imagining of a Sim I had played to explore TS3: University, where he was a Rebel and an art student, who ended up doing quite well in a series of artistic careers. This one clicked, and to draw in the cross-pack play, I introduced him to Lou Howell (a Maxis premade Werewolf with good genes) and, while I am not doing babies until after university (and having more of a handle on new lifestate and skills) I am already shopping for the expansion home to move into when they need a nursery and kids' bedroom.

It clicked not so much because I was "oh, yeah - Brannon!" but because when I tackled him in CAS the randomizer fairies smiled and gave me a great base to work from, and he turned out well enough for me to want to keep playing. That was it - that's what worked. For me, anyway.