If you have a lot of formulae in the workbook then you can reduce the
size by fixing these to values - Copy, Edit, Paste Special, Values etc.
Also, if you have a lot of named ranges which are no longer required,
these can increase the size of the file. In addition, you could check
on each worksheet what Excel thinks is the last used cell (CTRL-End),
as you may have a lot of excess rows or columns and these can be
deleted.
Hope this helps.
Pete