Always use dextrose instead of sugar in brewing. Dextrose is one half of the sugar molecule, missing the Fructose. Fructose can give your beer an off-cidery, 'homebrew' flavour. Use Dextrose to get a cleaner, crisper flavour.
Improve your beer further
To improve your beer further, try adding some additional malt to your beer to give it a better flavour and more mouth feel.
For Australian style beers, try a Brew Booster, with 25% malt, 50% dextrose and 25% maltodextrin (Corn Syrup).
For European beer and craft beer styles, use an Ultrabrew, with 50% malt, 25% dextrose and 25% maltodextrin (Corn Syrup).
Finally, try to keep your beer fermenting at a temperature below 25 degrees C. For tips on keeping your beer at the correct temperature, click here.