Rules of Thumb for Fill Factor

1. Read Only Table 100%
2. Table with minimum modifications over a year 90%
3. Table with slight to medium level of changes a year 70 to 90%
4. Table undergoing constant updates 50 to 70%

Remember to defrag your indexes regularly and make sure that your size you data files correctly to avoid file level defrag and whilst you at it start looking at ways to collect data about these perfmon counters on a regular basis.