During the descent, whenever I get drag required, it basically means that well... i need more drag on the aircraft in order to maintain my descent path.  I may be too high on the path descent when that happens.  Simply throw on the speed brake, and slow down to about where your flight director indicates and drag required will go off.  Thats the way I look at it anyways, im not absolutely sure its the right way (i think im at least warm), but it works for me hehe. 

To find out which runway to land, normally ATC arrivals will tell you (ie: "Expect ILS runway 34").  Or if your not flying with ATC for example, you will need to tune into the ATIS frequency, which will tell you winds and normally which runways are in use.  If they don't tell you which runway is in use, look at the winds, and find a runway that gives you a head wind.