first:
http://dwarffortresswiki.orgThe best way to use minecarts is quantum stockpiles. Make a feeder stockpile, a two tile track with a track stop set to dump at one end, onto a single tile quantum stockpile. Set a route that takes from the feeder, goes to the track stop, then returns. Everything from the feeder gets dumped onto a single tile. It's very good for FPS. Other than that, use them to transport things long distances, or as a weapon.
Magma smelting: the best way to do this really depends on your location. There are several ways to go about it, they break down to "bring the dwarves and ore to the magma" or "bring the magma to the dwarves and ore." It depends on how far down the magma is, and where it comes from (tube or sea.)
Military: At it's most basic, just get the best armor and weapons you can, put some dwarves in a squad, and let them train. See the military section on the wiki for more details.
New stuff: Each of these is a "location" and can encompass more than one room or meeting area. They all need constructed chests or bags in them, like the hospital does, for holding stuff that is used at that location. Create a dining room and assign it to a tavern location, designate any old area as a meeting are and assign it to a temple location, create a meeting room with bookcases, tables and chairs in it and call it a library.
Make musical instruments for use in the tavern or temple, make blank books or scrolls for the library, make goblets for your tavern. Musical instruments are procedurally generated, different for every civ. Parts can be crafted at a craftsdwarf workshop or smithy, then assembled at the craftsdwarf shop. To write books, you need to assign a scholar to your library, cook up ink from ash at the kitchen, grind up plants at a quern or mill, press them into sheets at a screw press, make scroll holders or quires and book bindings at the craftsdwarf workshop. Assign a scribe and he will copy books that have been written, either at your fortress or that you've bought from merchants.
That's the basics, but see the wiki for more details.