As Flintoide stated, rehearse putting it on and taking it off. You may want to watch a local college or pro team as to how they roll it out, unfold it, and move the tarp. You will need to know where you will be dumping the water when you take it off and make sure there is proper drainage in that part of the field or it will be a problem.
How to care for the tarp will determine how long it last. Dumb question, you also are getting a "tube" to roll the tarp onto.....
You will also need to have some type of notification system for the players to come and take the tarp off during the day (it is not a two man job), at lunch, or the morning so you can let the field air out and you can prepare the field to be played on.
Also, you need to constantly check the weather forecast carefully to determine when to put the tarp on or chance it and leave it off.