I don't have kids or step kids yet, but I do have have a step mom, so here's what I feel worked for her. 

The biggest thing is that she never, ever acted like I was anything other than her daughter. I'm 30 now, she met my dad when I was around 8, and from the day they realized they were going to be serious, she was like, "we're in this together, we're family and I love you unconditionally." To me, it seems tricky to do this while still honoring that you're not her birth mom, but just do your best. You already said you do that, but I think that was easily the thing that made the biggest difference. She and my dad actually have been separated for about 7 years and I no longer speak to my father, but I still talk to her. 

The other biggest thing I feel like, in parenting and step parenting and life in general, is listening to understand all the time. All people really want is to be seen and heard and understood, and it's a mistake I see people make with their biological kids and step kids and coworkers and friends and any kind of relationship that exists. My stepmom was FAR from perfect, but we've always been able to talk for hours on end and that's always made me feel connected to her, even when we didn't talk for a couple of years. 

Glennon Doyle talks frequently about her and her family's co-parenting experience, her writing might be a good reference to check out. She talks a lot about raising little people who will one day have to go out into the world and be full sized people who have to cope with life, and that's her biggest goal. 

Also, don't forget as parents it's not your job to be liked by your kids. It's your job to be a parent, and sometimes we don't like our parents.