A simple way to practice gunfights is to hop on a deathmatch server and try to get as many kills as possible. Important: Focus on clean kills, aim for the lower head and try to spray down enemys within the first 4-5 bullets. I would recommend you to play rifles like AK-47/M4A4/M4A1-S – if you want you can also practice your AWP skills. I would NOT recommend you to play on Valve’s official servers because these are “Team Deathmatch” so you can only kill players from the other team. Search for community servers with FFA, so you can shoot on everyone you see. Also a good practice is to play on headshot-only server. After some time, this will get you sharp aim.