Each action will have a <Task> section, which contains <Settings>, which contains a <Priority> element. The default value, for “below normal”, is 7. You can use either 6, 5, or 4 for “normal” priority. You will not usually want to go above “normal”. See http://msdn.microsoft.com/en-us/library/aa383512.aspx for more information on priorities. Quick answer: 6 will probably work for you.
0 REALTIME_PRIORITY_CLASS THREAD_PRIORITY_TIME_CRITICAL
1 HIGH_PRIORITY_CLASS THREAD_PRIORITY_HIGHEST
2 ABOVE_NORMAL_PRIORITY_CLASS THREAD_PRIORITY_ABOVE_NORMAL
3 ABOVE_NORMAL_PRIORITY_CLASS THREAD_PRIORITY_ABOVE_NORMAL
4 NORMAL_PRIORITY_CLASS THREAD_PRIORITY_NORMAL
5 NORMAL_PRIORITY_CLASS THREAD_PRIORITY_NORMAL
6 NORMAL_PRIORITY_CLASS THREAD_PRIORITY_NORMAL
7 BELOW_NORMAL_PRIORITY_CLASS THREAD_PRIORITY_BELOW_NORMAL
8 BELOW_NORMAL_PRIORITY_CLASS THREAD_PRIORITY_BELOW_NORMAL
9 IDLE_PRIORITY_CLASS THREAD_PRIORITY_LOWEST
10 IDLE_PRIORITY_CLASS THREAD_PRIORITY_IDLE