These tips are focus on the fundementals. Without these you have nothing.

1. Keep machines Cleaned, Filled and Working at all times.
2. There is no such thing as a "Pristine Account". All of the huge vending companies have them...I know because I work for one. Focus on smaller companies and wow them. Having a few great accounts is better than having 500 lousy ones.
3. Stop putting coffee vending machines in accounts, there is a gas station with coffee on every corner.
4. If you have a food machine check the dates often, I have seen our company get kicked out of accounts for having one out of date sandwich!
5. Fill the main flavors of soda to the brim (i.e coke, diet coke) the other flavors (sprite, orange, root beer) only fill half way. Alot of people will say they want these other flavors but these same people will stick with the main flavors.

I hope this has been helpful.