This script truncate all tables or reset all tables of a database. In this script a loop is running through a cursor which first get the list of all tables generated by user and then truncate all the tables.

Declare @t varchar (1024)
Declare tbl_cur cursor for  
select TABLE_NAME from INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE = 'BASE TABLE'

OPEN tbl_cur

FETCH NEXT  from tbl_cur INTO @t

WHILE @@FETCH_STATUS = 0
BEGIN
EXEC ('TRUNCATE TABLE '+ @t)
FETCH NEXT  from tbl_cur INTO @t
END

CLOSE tbl_cur
DEALLOCATE tbl_Cur

Note: Please take back of all data which you do not want to be deleted. This is for your data safety purpose.