The second I saw the name of this thread I immediately knew the mass of misleading/wrong information that would be thrown here. *sigh*
Go slower.
If you're not oversteering or understeering slightly through a corner, you're not going fast enough. If you're oversteering or understeering too much, you're going too fast. 
Not at all. One can easily make a car oversteer or understeer without being anywhere near the theoretical speed for that particular corner.
But seriously, less throttle on corner exits helps, but then this is likely more a problem for you in video games than in real life, unless your track whip has over 400 horses and not much grip. Generally you want to be straightened out as much as possible before you add gas.
Nope. I could slide my Miata around on R888s all day with an almost stock, tired 1.6.
And no, you dont want to be straightened out as much as possible before you add gas. Your foot should be on the gas pedal immediately after it's off the brakes. The more you unwind the steering wheel out of the corner the more throttle you give it. Depending on the torque output of the engine (and some other variables) will determine how many fractions of a second your throttle input should be in advance compared to your steering unwind.
IDEALLY, there should be no time gap between letting go of the brakes and the initial "getting on the gas."
There's not much practical I can tell you except practice, practice, practice. Get on the brakes later and later (but always straight, though with ABS, it's not such an issue as without) into the corner and on the gas earlier and earlier until the car starts to tell you otherwise.
No, no, and no. Practice does not make perfect. Only Perfect practice makes perfect. If you practice making mistakes you will only get better at making mistakes.
Always in a straight line? What ever happened to trail braking? And if you get on the gas and the car "tells you otherwise" maybe you should try being a bit less sudden with the initial input and smoother with the pedal's follow-through/more consistent with the steering inputs as opposed to assuming you've reached the limit on how soon you can get on it which, remember, should be immediately after your foots off the brakes.
Typically, in real life, you'll get understeer long before you get oversteer unless you're a total muppet on the gas pedal.
Or unless you're driving at the limit.
They're awesome
At lower speeds, it's easy to get oversteer, but in long sweepers and high speed corners, you're usually at the tires' limits and understeering... on a stock car. Personally, I prefer to lean a bit on the understeer through faster corners as that's a lot more predictable than trying to balance it out by inducing oversteer via the throttle or brakes.
On the contrary!
In slow, sharp corners, the rear wheels track to the inside of the front wheels. The resultant force from the rear wheels will "push" the front wheels towards the outside (understeer.) Unless of course you'd overdo it with too much gas and end up in an oversteer situation.
This is why you see autocrossers doing everything in their power to make a car understeer less with massive rear roll bars and what not.
In long, fast sweepers the opposite happens. The rear wheels track outside the front and the resultant force from the rear wheels tends to push the rear axle "around" the front.
And by the way, you should ALWAYS be at the tires limit regardless of how fast or slow the corner is. Given, of course, you have enough torque from the engine to take you to those speeds.
So my say in this is, aside from answering your question in the above replies, adapt YOUR driving style to the car. Not the other way around. Cars don't have bad habits or bad days and they certainly don't make mistakes. Come to an understating of what the car is really doing and, more importantly, what YOU'RE really doing/making the car do. It is just too often that people are completely misinformed in regards to the dynamics of the car (let alone what changes to the system actually do) and can never seem to figure out what they're doing wrong. In most cases they simply blame things on the car.
Go read yourself some books. I highly recommend the
Speed Secrets series as it is very easy to comprehend and is great with new drivers.
Somehow managed to forget where I last drifted a Fit...
