The first thing you probably want to do - depending on the restraints you set yourself - is create some safe edges to limit the number of angles cavern life can attack from. De-ramping is the quickest and cheapest way to do this.
If you don't use the dfhack command to increase squad training speed, then for melee use squads of 2 or 3 exclusively. Put their barracks (and beds) at the edges, so they train and defend simultaneously. Note that cavern life tends to be large, and unarmored. This means that sharp and penetrating weapons are good, blunt weapons are bad. Axes, spears and picks tend to be excellent and maces are appallingly bad. The other weapons (hammers and swords) will work reasonably.
Some Forgotten beasts will kill you no matter what you do (short of trapping them), but to maximize the chance of survival you should kill them from a distance with multiple squads of 10 marksdwarves. As a rule you should try to have every "civilian" except the miners and woodcutters in a marksdwarf squad, this will further harden the population against random intrusions and allow you to bring a great deal of firepower against threats.
You should try to arrange some decontamination trenches to keep important areas free of forgotten beast syndromes. This is as simple as digging out channels and filling them with 2/7 water.
Depending on how much you are intending to mine, you might need to rely extensively on leather and bone. Cavern wildlife will provide quite a lot of this in time, but you might want to bring a bunch of extra turkeys to bootstrap your leather and bone industry (at 6pt per turkey, vs 5pt per leather, turkeys are a pretty good deal - otoh metal bolts are pretty cheap to embark with if you embark with ore and coal, in fact they are cheaper than wood bolts if you have bit.coal or lignite and malachite or copper nuggets)