When you put up vending machines you need to ensure that the products are in sync with the location. If you are putting a vending machine at a truck terminal, maybe one that dispenses cigarettes, coffee, snacks and soda would do well. If you are going to place vending machines at a hospital, coffee, kids' toys, and healthy drinks and food might be more appropriate. At a gym, sell sports drinks or healthy non-fattening snacks. At a photocopying center beverages would sell fast. Take a look at what items are already being sold in the area where you intend to set up your vending machine and think of alternative products to offer.
However a critical aspect of the business is sourcing the vending machines. You need to have reliable vending machine suppliers. It's important to know how to deal with vending machine suppliers. Some will try to rip you off. Try and find a mentor who can help you and give you unbiased advice. Don't always take the word of vending machine suppliers, who actually want nothing but to make money from you. Ideally, look out for the manufacturers of the vending machines and try to deal with them directly.
There is another aspect which is critical and that is whether the vending machine supplier you deal with is also going to be responsible for the refilling of it. Find out whether the products that you need to vend can actually be sourced from the vending machine supplier at cheaper terms than you can source individually.
A bit of caution while running the vending machines is required. Machines need to be well maintained else they might malfunction and you might not profit. Vending machines need to have the used products repeatedly replaced. If you have electrically operated machines, it may pose a problem when there is a power cut. You also need to look out for thefts or physical damages caused by people who misuse the vending machines. Certain areas are going to be more vulnerable and physical security will be an issue you definitely need to address.