Simon from Surrey, BC has an absolutely flat backyard and the kids have to wear boots just to walk across the grass.
If it is perfectly flat you will have to do some landscaping, although not too much. In fact you could pull back the grass and simply put some soil under the grass to change the slope. You will probably want to create something like in the graphic, but much less noticeable. If you actually create a centre low spot, then you will want to dig down in the bottom of the swell and put in some drainage pipe as in the second graphic. This will receive the run-off and take it someplace, even to a dry well if there is really no place lower to drain to. A dry well is a large hole in the ground the size of one or two 45 gallon barrels that is filled with gravel. There is soil and grass over the top, but excess water flows to the dry well, which takes it off the surface and buys you some time for it to soak into the ground.