Run for the hills while you still can!
Just kidding, really, congrats!
First, set realistic expectations. The thinking is that how ever old the kids are when your family blends, that's how long it will take for everyone to really settle into a new normal. So if you have a 6 year old, it'll take 6 years. An 8 year old, 8 years, etc.
Know that even when you do everything right, it's HARD. If you each have exes in the picture who share parenting time, it's even harder. When conflict arises, you have to work especially hard to not unconsciously retreat to a place of "his" vs. "mine" thinking.
I think the biggest issue in our blended family is that when we got married, we didn't have custody of my step-daughter, who my husband puts on a pedestal and believes does no wrong. She actually is an exceptionally good person and always has been and never gives anyone trouble so it was hard to argue with his worship. So he really missed her during the week and worried about her and instead of getting to parent "his perfect princess" full-time, he got my oldest son, who has some challenging behavioral and personality traits that my husband just wasn't equipped to deal with day in and day out, so he subtly rejected my son. So this set up a "mom and C" vs. "dad" conflict almost from the day we got married where my husband always felt that I picked my son's side (because he was 5 so yeah...I'm going to support my little boy over a petulant adult man) and I felt like I wouldn't be constantly forced to defend by son if my husband would just stop picking on him. 10 years of this had just been great...
For practical advise, I would seriously seek out the counsel of a family therapist or counselor to help with the transition. Think of it as preventative medicine. Find someone who both you and your husband trust and like, let him or her get to know you, and start with hashing out the details on things like chores, routines, discipline, money, gifts, etc. With guidance, it's easy to set up the framework for your household in such a way that you remove a lot of the decisions and misunderstandings that can trigger conflict. Then if/when real conflicts arise that seem to really cut to the core of you or strain your relationship, you'll already have a trusted, private third party to help talk you through the conflict before you get to a point where damage is done. It's so easy to be protective and defensive of our kids and that can lead couples to say or do hurtful things.
Some may think that proactive counseling is over the top, but the success rates for second marriages with children are unfortunately not great, so I think it makes sense to go into this knowing that you will step on some landmines and are looking for ways to get some outside support and counsel before you do that so that you can manage conflict in a healthy way.