Before anything else, MyHordes (die2nite) is a bit of a complex game with a lot of possible actions. Some are benevolent, some far less, may it be for you or for others.
Don't be afraid of trying things yourself. Learn, die, and start over.
In MyHordes, death doesn't really matter.
Then, read this wiki. The more you'll learn, the fewer mistakes you'll make, helping both you and the other players stuck with you to survive longer.
Prioritize the community's interests and defenses: this is the best way to ensure a lengthy survival.
Read and participate in the discussions on the forum to stay informed and up to date on what your fellow-citizens are planning to do and how to organize (check the Workshop, Bank and Construction Sites topic as often as you can!)
Keep track of how many Action Points
you have left, to avoid getting stranded in the desert. Don't forget they're a limited daily resource…
Water is a rare and vital resource, use it wisely. If you're not taking part in expeditions and only spend your action points in constructions, it's recommended to only drink every other day.
Do not go in the desert alone without being aware of where the zombies are. Check the map beforehand (especially the amount of zombies!). You can organize “expeditions” with a group to make it less dangerous.
Never use objects without knowing what they do, how rare they are, or how useful they are to the community, or be ready to face the potential consequences of your experiments.
Personal upgrades require a lot of Action Points, especially at the start of a town. Some even use resources that could be used in construction sites. Make sure your fellow-citizens approve that investment or be ready to face the consequences.