By "flavour" do you mean more hoppy, or more malty?
Hoppy is easy - as brumbrew recommends.
More malty? Well, you could steep some grains of a crystal malt. This is basically a malt grain produced in such a way that the starches are converted to sugars. What this means is that you don't have to "mash" the grain in the way that an all-grain brewer would. You can extract the sugar - and the malty flavour - by steeping the grains in hot water. There are many different sorts available which will give a different effect. Your local homebrew shop might just sell "crystal malt" - which will be fine to try out, as long as it hasn't been hanging around for half a year. Otherwise, online suppliers are good (I most often use the Malt Miller)