I usually go 2 nights to ensure I can get there early to apply.
Some embassies will require proof of hotel reservation, flight out of Thailand, and proof of 20,000 baht. But, it depends on the consulate/embassy. Some can take longer than a day as well so, make sure you know what you're getting into before you book a flight.
Just to clarify Ben... You have to go to an embassy to get a 60 day SETV. So, plan accordingly....cant get one at a border crossing. And it takes a couple of days. Look through the forum posts.....hundreds of comments on which embassies in the region to use.
Vientiane Laos to get a new SETV as it's one of the few that don't require proof of onward flight, etc. Otherwise, Penang Malaysia or Savannakhet Laos are good options to purchase a new visa. Alternatively, you could border bounce by land twice and get 30 days each time (limit 2/year) then extend the second one at immigration in Thailand.
K.... ignore original comment.... never heard of a 6 month SETV. If you go out you will either need a re-entry permit or, when you come back in, you get 30 days (exempt entry).