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when doing deep sky imaging you should take dark frames and flat frames.
Dark frames are best taken at the same temperature your camera's sensor is at the time of imaging. so because you do not have a cooled ccd which you can set the temperature accurately, you should take dark frames either during or after your imaging session. dark frames should be taken at the same exposure time and ISO as your light frames. take darks with your lens cap on. take around 10 - 20. these frames will remove any consistent noise that is a part of the electronics at that temperature (noise is your enemy when trying to capture faint objects)
Flat frames should be taken during dusk or dawn (unless you have a light box). you can rack your focuser out and/or put a white t-shirt over the scope to create an evenly illuminated field. flat field images remove the vignetting, dust motes or other issues to do with your optical tube. i have found that flat fields are essential if you want to stretch your images and bring out subtle details, otherwise you are likely to end up with a uneven image that is difficult to correct. take 10 - 20 as a rough guide
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