It all depends on what you are trying to do.
First if it is really bowed you need to realize that then ends are going to end up much narrower. Set the board with the bow up on a flat surface and measure the highest point of the gap in the middle. The is how much narrower the ends are going to be from the middle of the board. Of course if that is acceptable then you can always straighten out the other side on the table saw.
One way to reduce the narrow ends problem is to shorten the board, cutting it in half will make it much less noticeable. But cutting it down much closer to final length will help, especially if cutting off from the side of the worst offender.
Then you just plane it, run it through and don't try to push harder to get it to plane more, you can make the cut larger to speed up the first few passes, but generally it's not recommended to go more than 1/8" at a time. Each pass will shave off a wider and wider section of the board and eventually they will meet in the middle (or near the highest spot).