Best Practice for getting contacts and accounts into salesforce and keeping it clean

[finnadat]

After lots of searching i haven't been able to find a "best practice" for how to get contacts and accounts into salesforce and keeping it clean.  Example, you have 100 cards from a tradeshow and if you import cards from an excel spreadsheet, salesforce isn't going to know that the contact goes into account X houston or london.  If you import them as leads, there isn't a way to merge updated lead information into an existing contact so my thinking is:

• search on name
  • if no name, type in new contact
• search for account with correct office location
  • if none make one, if multiples, merge them
  • the account question is interesting.  If the address info for the contact is left blank, it will propagate from the account (which is good and leads to less data entry errors) but you can only view the account and not the account location in the contact so you don't know if it is account X in houston or london unless you put that into the account name and it isn't the account name..
    • a way to resolve this would be to have account location available in contact pages but it isn't
• add as much data as you can and if there is an opportunity, make one

so if an admin assistant is given a stack of cards what is the best way to get them into salesforce?  There are 100 ways to do it but what is the most efficient method which reduces duplicates and erroneous data?