Q.  Besides a sign on the front yard and the MLS how else can a home be promoted to potential buyers?

A. Let me start of by noting that even just putting the home on MLS and a sign in the front yard can be improved and they must be improved: if the basics are not done well then it makes no sense to expand elsewhere.

The MLS (multiple listing service) now provides us with the opportunity to put up unlimited photos not like the 6 just a few years ago.
While a hundred or more photos may be a bit much, two dozen are just about right, but they also need to bell crafted photos which represent the property truthfully, but in a good light. 

Many still fail to put even one photo on the mls or good photos for that matter.
A good description can further be expanded with supplemental information like floor-plans, a list of upgrades etc.  Then there's an opportunity to attach videos and virtual tours.

The sign itself provides opportunities to expand the reach to potential buyers. 

Not every one is eager to call an agent to get basic information and putting up empty flyer boxes is actually a detriment to the sale. 
A rider with an address to a property specific website is a great addition or text messaging where a drive by viewer can quickly send a text and get an automated reply with the basic details of the home, including some photos.

Now if you have those basics covered there are dozens of activities that can be performed to get a home exposed and sold.  It's easy to look busy and it's easy to do stuff, but stuff does not sell homes, so whatever extras you do need to be ones that actually draw in inquiries from buyers.

While print advertising still has it place the online environment is the primary method of exposure.  A few things to consider.
Targeting: is one method of advertising to the most probable buyers for the home. 

This is further expanded by split targeting to different groups, first time home buyers have different needs and respond to different ads then second home buyer.

SEO or search engine optimization: making sure that buyers find the home online.

Networking amongst top agents remains an important step as most homes are sold by buyer's agent.

Open houses do sometimes word, but not for all homes.

Staging both inside and outside, no doubt, helps.  A home for sale is a product in a large market so getting the attention of a shopper by looking better only makes common sense.

Enhancing ads on many of the online home distributors helps provide more information.

Blogging, when done, well can be a powerful way to expose a property.

There are property specific website: websites made just for the home.

These are just some of the additional things that can be done, that work.

And let's not forget proper pricing: if a home is not priced for the market it does not matter how much you expose the home, it won't sell. 

Most buyers are very knowledgeable, especially with the information provided by their agents and online, so why would you expect them to overpay for a home.