I tend to give at least every other attack
some "flavor", at least a location and how "ouchie" it is. I really only get into long descriptions for big damage. As far as hit locations, I wing it if it's a normal attack, and I have a post-it with a humanoid stick figure and numbers for hit locations on my screen if I get into a "chest hit" rut. For criticals, I use a critical hit system ("Torn Asunder" from Bastion Press) that has not only hit locations for any conceivable body type, but specific effects for "really critical" hits. (Not to mention fumbles.) It's a great product. So, I
don't describe "crippling strikes" unless they actually
got one. (Solves that problem, for me at least.)
I think the most common (and understandable) problem new DMs run into is imagining HP as a static value, instead of a reflection of the ability an expert combatant has to
avoid damage. Think of it as a Dodge skill that you can't put any ranks into; it's the same thing the party rogue is doing with Evasion, the rogue is just better at it.
Otherwise, you have the image of high-level fighters carving great wedges of meat out of each other and archmages frying each other to small puffs of ash every six seconds which makes so many high-level D&D games so cartoonish. Also, that six seconds: A
lot can happen in a knife fight inside of six seconds. Avoid the "one roll, one hit" mentality and describe big (non-critical) damage as a series of strikes, rather than two guys standing around running each other through and then looking at their watches for five seconds.