Guidelines for index-fragmetnation

Some starting points to keep in mind for index fragmentation

•  If an index has less than 1000 pages and is in memory, don't bother removing fragmentation
• if the index has:
  • less than 5% logical fragmentation, don't do anything
  • between 5% and 30% logical fragmentation, reorganize it (using DBCC INDEXDEFRAG or ALTER INDEX ... REORGANIZE)
  • more than 30% logical fragmentation, rebuild it (using DBCC DBREINDEX or ALTER INDEX ... REBUILD)

 The guidelines are taken from 
http://sqlskills.com/BLOGS/PAUL/post/Where-do-the-Books-Online-index-fragmentation-thresholds-come-from.aspx