What is SPID in SQL Server

Here is the script to find out the average index fragmentation levels. Based on this value you can either Rebuild or Reorganize the indexes. Index should be rebuild when index fragmentation is great than 40%. Index should be reorganized when index fragmentation is between 10% to 40%. Index rebuilding process uses more CPU and it locks the database resources. SQL Server development version and Enterprise version has option ONLINE, which can be turned on when Index is rebuilt. ONLINE option will keep index available during the rebuilding.

SELECT DB_NAME(PS.database_id) AS dbName,
		S.name  AS SchemaName,
		O.name AS TableName,
		b.name,
		ps.avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL, NULL, NULL) AS ps
INNER JOIN sys.indexes AS b ON ps.OBJECT_ID = b.OBJECT_ID AND ps.index_id = b.index_id
INNER JOIN sys.objects O  ON PS.object_id = O.object_id
INNER JOIN sys.schemas S ON S.schema_id = O.schema_id 
WHERE  ps.avg_fragmentation_in_percent >= 20 -- Indexes having Fragmentation >=20
AND PS.index_type_desc IN ('CLUSTERED INDEX','NONCLUSTERED INDEX') -- Only get clustered and nonclustered indexes
AND b.is_hypothetical = 0 -- Only real indexes
AND O.type_desc = 'USER_TABLE' -- Restrict to user tables
AND PS.page_count > 8 --- ignore tables less tha 64K
ORDER BY ps.avg_fragmentation_in_percent DESC

Here is the script which can be used for Index rebuild, you can schedule this as a daily/weekly job 

SET NOCOUNT ON
DECLARE @dbName NVARCHAR(128)
DECLARE @SchemaName NVARCHAR(128)
DECLARE @TableName NVARCHAR(128)
DECLARE @IndexName NVARCHAR(128)
DECLARE @avg_fragmentation_in_percent FLOAT
DECLARE @nSQL NVARCHAR(4000)
DECLARE @index_list TABLE(dbName NVARCHAR(128),
						  SchemaName NVARCHAR(128),TableName NVARCHAR(128),
						  IndexName NVARCHAR(128),avg_fragmentation_in_percent FLOAT )
INSERT INTO @index_list
SELECT DB_NAME(PS.database_id) AS dbName,
		S.name  AS SchemaName,
		O.name AS TableName,
		b.name,
		ps.avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL, NULL, NULL) AS ps
INNER JOIN sys.indexes AS b ON ps.OBJECT_ID = b.OBJECT_ID AND ps.index_id = b.index_id
INNER JOIN sys.objects O  ON PS.object_id = O.object_id
INNER JOIN sys.schemas S ON S.schema_id = O.schema_id 
WHERE  ps.avg_fragmentation_in_percent >= 20 -- Indexes having Fragmentation >=20
AND PS.index_type_desc IN ('CLUSTERED INDEX','NONCLUSTERED INDEX') -- Only get clustered and nonclustered indexes
AND b.is_hypothetical = 0 -- Only real indexes
AND O.type_desc = 'USER_TABLE' -- Restrict to user tables
AND PS.page_count > 8 --- ignore tables less tha 64K
--ORDER BY ps.avg_fragmentation_in_percent DESC
SELECT TOP 1 @dbName=dbName,@SchemaName=SchemaName,@TableName=TableName,@IndexName=IndexName,@avg_fragmentation_in_percent=avg_fragmentation_in_percent FROM @index_list
WHILE( @@rowcount <> 0 )
BEGIN
    IF @avg_fragmentation_in_percent <= 40 -- REORGANIZE
            SET @nSQL='ALTER INDEX ' + @IndexName + ' ON ' + @dbName + '.' + @SchemaName + '.' + @TableName + ' REORGANIZE;'
    ELSE -- REBUILD
            SET @nSQL='ALTER INDEX ' + @IndexName + ' ON ' + @dbName + '.' + @SchemaName + '.' + @TableName + ' REBUILD WITH (SORT_IN_TEMPDB = ON, STATISTICS_NORECOMPUTE = ON, ONLINE = ON, MAXDOP = 0);'
	BEGIN TRY 
		EXECUTE (@nSQL);
    END TRY 
    BEGIN CATCH 
		SET @nSQL =  REPLACE (@nSQL, 'ONLINE = ON,','')
		EXECUTE (@nSQL);
    END CATCH
    --PRINT @nSQL
    DELETE FROM @index_list WHERE dbName=@dbName AND SchemaName=@SchemaName AND TableName=@TableName AND IndexName=@IndexName AND avg_fragmentation_in_percent=@avg_fragmentation_in_percent
    SELECT TOP 1 @dbName=dbName,@SchemaName=SchemaName,@TableName=TableName,@IndexName=IndexName,@avg_fragmentation_in_percent=avg_fragmentation_in_percent FROM @index_list
END