There are many good choices. Playing as pellik suggested will certainly do the job.
Other choices I would consider are to play 1...e5, 2...Nf6, 3...Nc6, and 4...Bb4 (assuming White has played Nc3). Check out some of Karpov's games in this line, for example Lautier-Karpov from Linares 1994.
Or, you can play symmetrically (1...c5, bring out the knights to c6 and f6, fianchetto the KB, and play for ...b5 with ...a6 and maybe ...Rb8). Efim Geller won some nice games in this style (I have his book The Application of Chess Theory).
Hey, so I recently played a 2300 USCF rated player who employed the english opening, and even though it was a close game, i played an awkard hedgehog system, mostly because i was unprepared for the english. I was planning on studying a system against the english but i was unsure of what system i should look into to. For example, should I study the hedgehog, or the Botvinnik system reversed or some other system. In addition, i am a more aggresive player but i don't mind playing a more positional system. Thanks