In buying a short sale, there really isn't much a buyer can do to speed up the process. As long as your agent requests updates and is confident the list agent and their negotiator is on top of the bank, that's about as much as you can do.
If the timeline is of concern, you may want to find a short sale that only has one lien holder (bank). While every short sale is different, some banks can be faster in getting through the approval process. Also, some short sale properties have already gone through the approval process and can be a matter of weeks to issue a new approval letter. To be honest, if you truly love the property, you just have to wait it out.
Foreclosures do not have the waiting period that short sales do. You typically get a response from the bank within 72 hours. Depending on the amount of counters back and forth, you could close on a foreclosure in roughly 30 days. Short sales can typically run 2-4 months depending on the lien holders (banks) and how many there are.