Setting boundaries has worked well for me as has accepting that I can't change the situation, but I can change how I react to it and how I let it affect me.  

I guess you mean something other than the giant meltdown, snot blubbering, crying episode? Well, that got DH's attention anyway.

My skids were adults when DH and I got married, so never any expectation of parenting. But adult skids bring a whole bucket of other issues. Becoming invisible when they were around, spending money we didn't have, chasing after their affection were/are my major issues.

Individual counseling for both of us, and through that I learned how to set and maintain boundaries. And I stopped trying so hard to get them to like me. That took off so much pressure from all of us. I think they appreciate that their dad is happy (and that puts them way ahead of some other adult skids), and they are generally civil. The very few issues we ever have any more are almost always caused by DH, and we deal with those through gentle conversation and reminders of what I need from a spouse.

Being flexible about holiday celebrations has worked for us.  Our BM was rigid about having Thanksgiving and Christmas Eve, and not only the date, but wanted everyone there at a specific time for a sit-down meal.   This seemed to lead to lots of frustration for her because out-of-town job commitments, small kids and just general immaturity meant that her plans were always getting snarled (meaning she would have one of her meltdowns).

I felt sorry for the SKs, they were trying to please her and also their spouse's parents.  So we often had Christmas a week early and had kind of an open house/ buffet format.  "Just come sometime after x o'clock".  We tried to time Santa's visit (one of the sons disappearing and reappearing in costume) and gift opening to whenever they had all arrived.  I also urged everyone to only gift the grandkids whereas at BM's house they continued to gift each other altho I knew some couldnt afford it.

To me, it wasn't about the meal or meeting any Hallmark expectations, it was about us all together in peace once a year.

Really.. Number ONE should be.  TIME... give yourself plenty of time to let these relationships develop and do NOT cling to a bad decision because it took you so long to make.  Rushing to live together.. rushing to have a child (or not preventing that).  Make sure you have a much better idea of what you ARE getting into.  No, you can't predict it all... but in almost all cases on here, I think most steps saw some flags in advance but chose to ignore them for whatever reason.

Number TWO?  Should be patience, flexibility and ability to compromise.  I know it seems unfair, but generally, due to the nature of steplife, it's more likely that the Stepparent may need to compromise or adjust to the differences presented by their partner's child situation.   No, I'm not all "first family" and the SM has to suck it all up.. but there will be last minute changes that can't be avoided.. there is the fact that you are not only entering into a relationship with your partner.. but their children and their EX by extension is a relationship too.  It's a fine line but you should feel like you are a priority to your partner, but you have to accept the obligation to their children and understand that their needs.. may become priorities as well.. and that you partner has to manage them.

Three?  Thick skin... if you are easily bothered/offended/rigid or controlling.. steplife will be super difficult... and make no mistake.. it is a CHOICE.. you are choosing this life.. and you can choose to leave it behind as well.

4. Collaboration  between equity life partners.

5. Zero tolerance for crap from kids, Xs, family, etc... Immediate confrontation of deviations from behavioral and performance standards putting the ownership and onus for consequences on those who earn them.

6. NO! Is the most powerful word in the SParent's vocabulary.  Use it.

There are major problems in there relationships.  Really happy people are too busy having the time of there life to write on this board.

Step life is hard and emotional. Someone loved  another person enough to have kids with them. That life exploded. 
so one partner is looking to replace the ex. The other partner wants to be love, respected like the ex.  Have like a life the ex had,      Unfortunately the ex had no ex,or SK  to deal with.  
The ex got candle light dinners, romantic weekends away, mini vacations, money to buy nice things.

You get weekends cooking for SK. A SO wanting to control life to get there big happy family with out thinking about there SO. Talking does no good.  What does that leave you with. If there a fourth choice  I don't know what that is  except leaving everything the same and suck it up,  being used and unhappy 

No idea all that worked in my steohell was total disengagement and hard boundaries.

I did counselling in the early years, both with DH, and my own and it was lifesaving. I've never thought of running, as I love DH too much, but that has made me feel very trapped at times and in the early years. 

Whatever you end up doing, I don't think it's just one approach for the whole stretch. I've been a stepmum for 14 years now and my approach has evolved over time. It started out with idealistic and naive hopes and throwing myself in the deep end by being actively involved from the very beginning. That lead to years of anger, resentment and depression. 

Following counselling and letting myself off the hook from the pressure I put on myself to love my skids, it gradually got better over time and I stopped dreading the time with the skids although I've never gotten to a place of looking forward to it either. It will always be something I have to endure ie a bit of a chore. 

Since having my DS 3 years ago it's changed again. Initially it gave me somethingn to bond with SD16 over as we have never had anything in common and clash. However, over time I've found my resentment growing again as I'm obviousy more tired these days with a young kid and I don't want to spend time and effort on my skids (especially SD16) as I just want to focus on my DS. It's lovely when it's just the three of us and crazy busy when it's the five of us. 

In the end I've gone for two different approaches with my skids. I see SS15 as part of my family and I love him but I've given up trying to bond with SD16 - it's never going to happen as I just don't like her, never have and never will. So I've partially disengaged there. The disengagement is not overt, I'm still active in her life but I've stopped doing a lot of stuff I used to do as it was never appreciated by her or BM and I've stopped caring about the outcomes for her. She will have to live with the consequences of her poor choices. As long as it doesn't impact me post high school, ie I'm banking on her living full-time with BM (right now it's 50/50) then I don't care what she does with her life.