Golbat has mediocre stats all across the board, and has a sub-par movepool. A major weakness to three very popular types (Psychic, Ice, and Electric) hurts it as well. Golbat is best used at the end of the game when a majority of the opponent's Pokemon are paralyzed, but even then, Golbat is not a sure thing to sweep because of its inability to hit anything hard enough. It can work, but there are much better options for late-game sweeping than Golbat.
Switch Golbat into a predicted Earthquake, or something it can beat, and then Screech the opponent. If it's a slow Ground / Rock type, you may want to confuse it as well. Then, do what Golbat should do: hit something with Hyper Beam. Use Double-Edge if you don't like recharge turns, but beware of the recoil damage. Use Mega Drain on Rock / Ground types that resist your Normal-type attacks. Confuse Ray works well for parafusion when most of the opposing team is paralyzed.
Substitute can help the parafusion combo, and Haze can remove boosts versus things like Slowbro. There's nothing else otherwise.
Checks and Counters
Golem and Rhydon will resist Golbat's Normal attacks and only take about 40% from Mega Drain, leaving Golbat open to take a very strong STAB Rock Slide from either of the two. Gengar has no problems with any of Golbat's attacks, and can hit back with Thunderbolt or Psychic. Exeggutor resists Mega Drain, has the Defense to survive Double-Edge, and hits back with a STAB Psychic. Alakazam and Hypno hit Golbat with a STAB Psychic, and take very little from any of its attacks. Even Water-types take very little damage from Mega Drain, and most can hit Golbat with Ice Beam or Blizzard. It doesn't take much to take down Golbat.
In UU, which is where you'll see Golbat most of the time, Mr. Mime could scare it off if it is at full health and Onix is also a counter if Golbat isn't packing Mega Drain. A high HP Pokemon like Wigglytuff would also be able to do the job, especially since Wigglytuff can slow it down with Thunder Wave. Any UU Electric (namely Electrode and Magneton) would also be able to counter Golbat.