A good one for pre season and through the seasoning general is this.
Starting at the edge of one penalty area, run to the edge of the other area in >15 seconds. However long it took you is the rest period that you have (ie, if it took you 14 seconds, you have 14 seconds rest). You then repeat this another 5 times (6 runs in total).
After this set has been completed, you then have a 1 min 30 rest before running from penalty area to penalty area and then back again (2x lengths of distance) in >30 seconds. Once again however long it takes is the rest period. This is completed 6 times and another 1 minute 30 rest at the end.
Finally (you guessed it) your distance increases to 3x lengths, in a time of >45 seconds, with the same rule for the rest periods. 6 sets again. This is the last set so it will be very difficult, but this is the stage where you will feel the most benefits long term!
Enjoy