The best advice I can give is: plan for failure.
Your fort will eventually crumble and die. The point is to postpone that inevitable fate for as long as possible.
A lot of the time we plan for success. But in this game, the power of positive thinking will kill your dwarves. So a couple of examples:
Building a well:
Planning for success: as soon as this well is finished, I'll designate a drinking zone.
Planning for failure: if the water source freezes, that will boost the water pressure here, so I'll build a floodgate. No, better make it a bridge so if the water dries up, letting the goblins into my fort, I can still seal the chamber. And before I fill the aqueduct to the well, I should expect it to flood. If it does flood, how can I prevent it from descending my stairwell and flooding everything below it?
Building a wall:
Planning for success: when the wall is finished, no goblins will be able to get in!
Planning for failure: wall's almost done - I think. But I see a lot of people on the forums saying that they've missed holes in their defenses, so I should put a secondary wall up, and maybe a tertiary wall, and a moat, and a bridge, and train a couple squads ...
Building a pump stack:
Planning for success: pumping magma is just like pumping water, but this way I can use magma forges on the surface!
Planning for failure: this is going to explode in my face the first five times. Time to take notes so I don't repeat the same mistakes.
Training a Squad:
Planning for success: finally got them to spar, and train, and use weapons. Job's done, now to just wait while they get better at their skills.
Planning for failure: if I were a goblin squad, I would ambush right about now, when the military is at its weakest. What can I do to make sure they don't kill my civilians?