Correct surface drainage is the first place to start when tackling a wet baseball field. Sub surface drainage can be very useful, but it's slow compared to surface drainage, and more expensive to correctly implement.
Ideally a dirt infield will be crowned in the middle with a half percent slope in all directions. As much as a one percent slope is acceptable. Much more than one percent slope can impact the play of the ball, and cause the material on the field to migrate very quickly. As you move into the outfield we recommend increasing the degree of slope to 1 to 2 percent. In the outfield a greater slope is almost unnoticeable. When a field is crowned this way pay attention to where the water is being pushed. I've seen a number of fields that have standing water in the dugouts, and by the backstop. Some means of routing this water will need to be installed.
The other problem with the crown method is that it's not always possible. If you're installing a complex of four fields with the back stops in the middle you'll have a great deal of water going to the center, and it will be very hard to manage. Other times fields are built on land that is not been rough graded. In this case you have to work with the existing grade. Generally that means you're sheet grading in the same direction that the surrounding ground slopes.
We find a number of fields need to be graded so that the home plate is the highest point of the field not including the mound. Then we grade the field to a half percent slope away from the home plate toward the outfield.
We always recommend adding infield mix when you're grading a field. Minor grade corrections can normally be achieved with one 20 ton truck load of infield mix. Fields that have been neglected for a long time could need many more. Three to four 20 ton truck loads will make significant changes to the grade of the field.
If your drainage plan includes drainage tile you MUST use the correct backfill. In Ohio that means you cannot put the dirt you dug out of the trench on top of the tile. That dirt is almost all clay, and it will not let the water pass through fast enough, and it will quickly plug up the tile. If someone else is installing the tile for you make sure they remove the existing dirt, and truck in clean materials to back fill the trench. I fix this problem about once a year, and it's an expensive procedure.