There are many ways to do both more effectively… Things like usability studies and deep effective long tail keyword research will yield far better results. However, the short and narrow of it is to create usable content. Other wise you might win the battle and lose the war!
Recently, there has been an abnormally high amount of buzz regarding the use of keywords in your urls. We have know for some time that this is likely to provide a small amount of weight for ranking. However, until recently it was pretty much guesswork.