Some people are having great success, but there are no secrets. Most of the problems are occurring randomly in the cloud, and probably have to do with "hotspots" in the databases there. Consequently when the problems occur, they hit different people randomly. Very little that can be done on the customer side to avoid these issues.
The company is very aware of the issues that have said they are making improved reliability their top priority.
I believe their sincerity, but they're not there yet. Search the forums for "reliability" or "stability" and you will find many discussion threads. But unfortunately no magic answers.
There are some things you can try in case it is a problem you can solve:
And it's always a good idea to get in touch with firstname.lastname@example.org and see if they have any specific suggestions.
But there still some cloud issues that just randomly get different people at different times. For that we just have to hope that the company's efforts to improve stability will succeed.
In the meantime, each person has to decide for themselves which specific use cases they want to trust to the current state of the system. Personally, I now only use SmartThings for convenience cases like a notification if the guestroom window was left open when rain is expected. I've moved critical functions over to other systems for now.
SmartThings remains my favorite home automation system when it works as intended, but personally I just don't find it reliable enough for anything critical right now. I do hope that will change in the future.