If you don't want to build a fort with dozens of z-levels worth of hallways and so on, just plan a fort with a set number of levels.
Dig down far enough first to place the levels, one for living areas/leisure/dining halls, one for workshops, one for stockpiles and one for farming. That's pretty much the basic needs for a fort covered in 4 z-levels. That shouldn't be TOO bad, right?
Anyway.
Easy ways to ensure fort safety huh, a wide and long enough entrance tunnel. Possibly with traps at the start. Cage traps work wonders to reveal ambush squads(except for kobolds and other trap-avoid races), weapon traps can soften up the enemy while your soldiers are still going there.
If you're feeling like challenging yourself, horrible traps of mass-death. With a brook it's quite easy to make a drowning-trap on your entrance tunnel. Just make a raising bridge to seal your fort entry path from the flashflood and drown all who are in the entrance tunnel. If you're feeling insane enough, use magma instead. Another option: Use a flashflood device, but it pushes enemies down a deep pit, breaking them apart once they hit the bottom. About 13-15 z-levels of drop does that.
Make use of your military-skilled migrants! This is important, these days it's a lot harder to train an able military than in 40d. But if you got some dwarf who shows up with previous military ability, use him as a squad leader for your raw recruits who haven't ever held even a pick or a woodcutter's axe. He'll be giving them lessons and eventually they will begin to spar.
If you REALLY want to, you could always construct a Danger Room. Read up on the Wiki on those, but the short explanation is: Put low-quality training wooden spears in your barracks as spike traps, connect 'em to lever, have someone pull the lever on repeat, your soldiers will gain EXP on various military skills fast as FUCK. I got legendary fighters out in a few months thanks to the Danger Room.
The caverns are dangerous, keep 'em sealed and make sure you have some way to seal parts of your fort if you got stuff like a well taking water from the cavern lakes. Flying forgotten beasts can easily fly up from that well. I know, I had two flying monster-birds in a row use the same god damn route. If you must use the caverns for something, build an airlock with a raising bridge.
You can NEVER have too many barrels, only too little booze or food. Keep a lot of barrels on stand-by at all times, and try to stay up-to-date on how many plants you currently have and if they should be brewed to booze already.
Lye-making is a tad borked right now, so bring 1 unit with you on embark for easy soap. You never know when disaster strikes and your important dwarves might be in danger of getting an infection. Just one unit is enough, right now barrels with 10 units of lye(bought from caravans) end up only producing 1 piece of soap. I assume that shouldn't happen.
Build a well ASAP. Possibly a water reservoir as well and empty some pool in it. Alternatively, breach the caverns and place a well above a cave pool. You never know when you might need some water. They also come handy if by some chance you would end up without booze. So you know, your dwarves wouldn't go walking all the way out of the fort to some puddle to get a drink and stumble on a goblin ambush squad.