Hmm..
Starving to death rarely happens in decent climates. If you're playing in a sinister tundra like Nist Akath, I could see it happening unless you got a good stable farming plan started early...anyway...
It's probabally somthing you'll see one day and go "D'oh!" over, but here's a few things to watch:
-Make sure you always have plump helmets turned to "off" for cooking and (early on) brewing. This way every plump helmet eaten will drop seeds, and you will never run out.
-Make sure plants are not rotting in a field. This might seem odd, but a 10X10 far might be TOO big--if your farmers keep planting new seeds rather than harvesting grown plants, you will waste them and starve. Make sure when you see plump helmets blooming in your field that you have at least one dwarf pulled away from his/her normal tasks to gather food. All dwarves can gather from the farms, even children and nobles (unless this has changed?) but until you have them in your fortress you will need a dedicated food hauler/plant gatherer.
-Don't underestimate harvesting plants from the surface. It's quick and those lousy immagrants can do it. It's also waste-free!
-Make sure you have a food stockpile close to your farm to store your crops in, as well as barrels to reduce the wear on food from dwarves walking over it (and the added benefit of taking up less stockpile room)
-Sell all of your stone crafts for all of the meat/cheese/fish/plants you can get your hands on. Free barrels and you will never go hungry.
-Be sure you have a working fishary, butcher, and kitchen to turn those occasional kills into stacks of turtle biscuits.
I know these might all seem obvious, but we were all newbs once and the occasional newbie might wander in here and find them extremely helpful.=p