Generally a smoother reaction as a flatter pattern has more wet/dry. It really varies though depending on the other lane factors. In Vegas I've had to go to my stronger equipment with quicker response to friction as most places seem to be lower friction with a few exceptions.

Hit what you're looking at.

 

I just posted this on another bowling messageboard, it is from Rich Jacobson:

"first and foremost on EVERY lane you bowl on, ALWAYS find the too much hook zone, then find the not enough hook zone. Split the difference. Then begin fine tuning with your bowling bag, super fine tune with your game changers if needed; hand position and speed."

On super flat patterns, there will usually be too much hook inside and not enough hook outside - find the area that (as Jacobson says) splits the difference and as itsallaboutme posted "hit what your looking at". 

That is how you attack a flat oil pattern.  Or conversely, you can do as I and spray and pray and hope for a miracle.

A different way to look at it.....

At the beginning, you will want a smooth reacting ball for the fresh as others have stated.  For me, I start with the same ball no matter the length or ratio (Venom Shock).  I may adjust the cover depending on the volume of conditioner.  I will try and play as straight as I can and adjust equipment if the Venom Shock is too strong or too weak.  I don't want to play left to right since that can introduce high splits and 2-8-10s. 

As the pattern begins to break down and a hook spot is developed, I will transition to a ball that has a little more backend then the ball I am using when the angles start to get too steep.  Most of the time I will transition to a stronger ball.  You will have to experiment to see what works best for you.

You can use whatever method you want to determine where to start on the fresh whether it be length-31 or whatever.  But one thing I always do in practice is try something around the track area to see how much effect the track will have on the pattern.  Many times you will be surprised at what is available there.

The only thing I will add to some already good advice is to stay as straight as you can as long as you can...and hope that everyone else on the pair is doing the same thing.  If 6 of 10 bowlers are doing different things, flat patterns can get "fun."

But isn't about having 'fun'?