When you’re in a low light situation and can’t or don’t want to use your flash, try these tips to get better photos:
• Use your camera’s highest ISO level to capture more light.
• Shoot in RAW so you have better control over the exposure later on.
• Try shooting in aperture priority mode using f1.8 or lower.
For more advice, check out How To Get Better Digital Photos In Low Light Conditions Without Using A Flash by Darren Rowse at the Digital Photography School.