Don't board the bus at Central Station on it's inbound journey to Queen Street and Buchanan Bus Station.
It is not a circular route and the driver would probably charge you twice and throw you off to the back of the line to board when the bus terminates at Buchanan Bus Station.
Board it on it's way back out from Buchanan Bus Station.
From Queen Street board at North Hanover Street (the side entrance to the station) and at Central Station board at St Vincent Street (1 block North of the station).
All Edinburgh to Glasgow trains are just turn up and go commuter trains.
Fastest are the ones every 30 minutes to Queen Street. They stop at the High Level Platforms at Queen Street. Next fastest are the ones to Helensburgh Central which are also twice an hour and stop at Queen Street Low Level, the trains to Central are twice an hour with a few extras.
It doesn't really matter which you catch- the time differences are small.
Maybe the smartest way is the City link 900 express bus from Edinburgh Bus Station to Glasgow Buchanan Street Bus Station then the #500 from its origin at Buchanan. Barely any slower.
Buy a £10 day return from Edinburgh and just don't return. The 900 runs every 15 minutes as a turn up and go service.
Another train route is the Helensburgh Train to Partick (2 stops beyond Queen Street) then the #77 bus through the Clyde Tunnel every 20 minutes.
If staying in Glasgow City Centre that night look for any of the City Centre Premier Inns.
If at the Airport the Holiday Inn or the Holiday Inn Express or even the Premier Inn.
