I think challenging yourself with some new form of gameplay, be it a family dynamic, story idea, life-state, etc. that you haven't experienced before can really work a treat. For me, I've invested a lot more time in a new family and have styled them to be a brand new legacy for me to work through. Usually I would go out of my way to save sims from death if they're doing something silly, or if there is a hazard like a fire, but I haven't this time around because it means that there's a shake up in the dynamic of the family I am playing and I find that to be the most easiest way to keep myself interested! :)