Even though I spoke about a lot of the bad aspects of the smoker, he was my personal choice. Using the smoker at peak effectiveness requires the patience to not just attack because you have an opportunity to, but to attack when and where you will be most effective. There are a few real good places to use a smoker on each map where you can stop the survivors advance cold even if you attack alone, you have to make sure when the survivors approach those "smoker havens" you are alive and ready for them. A few smoker tips...

1) Don't be afraid to stay in spawn mode for a little and follow the survivors. The smoker gives audio and visual cues to his position and sometimes you are best suited to wait a bit to spawn.
2) Identify the key locations for a smoker to have the maximum effect and prepare them for your dirty work. It's worth your time on map 04 no mercy to destroy some doors ahead of the survivors advance and destroy the railing on the 3rd floor so you can pull suvivors down and make them backtrack. On blood harvest map 01 pull a survivor off the hill and make them hang on to the edge of the chasm when they approach the rope bridge.
3) Don't be afraid to be a distraction to allow the other special infected to be more effective. Sometimes your job is to die so the other infected can do more damage. It's a team game, don't be afraid to take one for the team if that's the best thing in a particular situation.
4) Sometimes it's better to run away and go into spawn mode again then it is to make a worthless attack. You can also effectively trick the survivors with them thinking the smoker is behind them and then magically "re-appear" in front of them to drag one from a position they didn't think you could be at from where they "knew" you were.