Sports League Photography
If you are using a tent, make sure to set it up in the north-south position to keep the morning sun out and shadows consistent throughout the day. You will get the best light if the opening faces north.
Use enough light so your subject's pupils are fully open and keep you flash off-center.
Indoor Ambient Light
Close blinds and turn off overhead lights. Overhead fluorescents can turn your photo green; incandescent floor lamps can turn your photos yellow.
If using a window for lighting, use a north facing window for the best light.
Use a tripod and set your camera to the lowest noise rating possible.
Depth of Field
Remember this is an inverse relationship: the larger the opening, the shorter the depth of field. 16 is a small depth of field; 2.8 is a large depth of field.
And, as always, plan ahead with regards to equipment so you have time to become familiar with it before you are on a shoot.