In answer to the OP, the answer is quite simple.
Temp control, temp control, temp control.
Sure there are heaps of other variables as the guys say, but this is the biggest.
The reason homebrew gets twang, gets fruity gets esters, gets fusel notes is because your yeastie beasties in the drum are being cooked too high.
Get a Fridgemate, or a Tempmate, a manual fridge controller, or a thermostat, or a timer, or a heat pad thermostat, or an submersible aquarium heater, or simply forget the gear and brew in ambient temps that match the spec of your yeast (lagers in winter (when it's 10 degrees in the shed), ales in summer (when its 18-22 degrees)) then you'll hit the motherlode and get clean yummy beer.
Not sure what the temp range is for your yeast? Check the packet. Or better still, go to the Brewcellar, Wyeast, Fermentis or Whitelabs site and grab all the technical info on how to handle that particular yeast. Also realise that Brewcellar yeasts are actually repacked Fermentis yeasts. So if you're using European Lager Brewcellar, check the Fermentis guide for W34/70. If you're using American Ale Brewcellar, check the Fermentis guide for US-05. And so on.
Yeast handling and good temp control makes cleaner better brews. Bad yeast handling and temp control makes sharp tasting ones. The moment I realised this my beers went from the taste of toenail polish to clean heaven. Give it a bash and you'll see.
Hopper.