Beth Bowers has posted a great set of tips for MAS 90 and MAS 200.l  I've reviewed this and can say they are some of the most popular questions we get.
Topics included but are not limited to:
  •  printing daily transaction register updates if you didn't say 'yes' when asked the first time
  • Dealing with fractional units of measure and the use of EACH
  • Managing access rights of employees within date ranges
  • Attaching any type of document via memos.  This includes attachments to forms such as an invoice or purchase order
  • How to save personalized report settings
  • Dealing with the infamous problem in AR where invoices appear to already be paid in full when they aren't
  • Dealing with "Check Printing is already in progress" messages
  • Copying masterfile information from one company to another
  • Dealing with "Error 65"
And more.  See the full post here