This is long but very thorough. I play no traps/no turtling/extra attacker civs so I rely on military intensively:
NCommander's Ultimate melee guideA quick summary:
- Get in the habit of taking two dwarves from embark and/or a third of your first migration wave, and set up your first squad for training. Don't worry about teaching, or discipline, or prior military background yet - that's all min-maxing, and interesting for advanced players, but it is really NOT necessary. They'll train just fine without it!
- What is necessary is establishing the habit of setting some dwarves aside early, and getting them training non-stop. It's a wall of initial set-up to get squads started and equipped - follow NCommander's screenshots - but it's followed by virtually no management whatsoever, if you've done it right. They just train.
- For vanilla DF, for no turtling, no traps defense, I recommend a military to civilian ratio of 1:4. The key thing is training and armor - the earlier you start training, the more badass the dwarves will be, keeping them ahead of the threat curve, and minimizing losses.
- Start with making them non-metal armor sets, then move up to metal armor later. Metal is heavy and slows down training early on. If you start your training early enough, they'll be ready for metal armor by the time you've got a metal industry going (assuming you don't embark-allocate with one ready).
It is totally possible to mow down 100's of goblins per siege within a few years of embark with just a few squads of melee military without the slightest reliance on traps, bridges, animals, or marksdwarves. It is really only a question of getting them drafted, equipped, and training early. The trade-off is a labor-deficit on early fort development that you'll need to mentally hurdle, and bruising your brain a bit with the military screens - which thankfully are mostly set once, and forget.