Love their mother.
Not always realistic for divorced families...but definitely model civility and kindness and don't say negative things about mom!
My stepdaughter ADORES her dad, and my biokids love him too because
a) he is reliable - he is almost always at every single school or extracurricular event
b) he is THERE - if they need something or have a question, he stops and helps. If they need a ride or want half a dozen friends over, his answer is almost always, "sure, I can do that"
c) he teaches without lecturing, and he loves to share his talents with them
d) he learns about the things they love. He is genuinely interested in them, and they can tell
e) he doesn't assume kids are stupid. His goal is to teach them how to make good decisions on their own, not to make all of the decisions for them
f) he doesn't tolerate BS and he doesn't lie or fib to the kids.