As many of us live in light polluted areas this is a quite common question.
Some steps to help are:
- Make a light/dew shield for the front of your scope. This should extend 1.5x the diameter of your mirror in front of the focuser and will help stop ambient off axis light getting into your focuser and reducing contrast.
- Make a baffle for the rear of your scope if light can get around the mirror. A simple ring set up here will do and can be made of plastic. Again, it will stop ambient light getting ito the scope. Not so important as the light shield but easy to do so worth the effort. Make sure there is room for air to flow around the mirror still.
- Flock your scope's tube. If ambient light still gets in, and it will, flocking will reduce the effect on contrast.
- Make like a pirate. Get an eye patch and put it on your observing eye for a good half hour before observing. This will allow your eye to dark adapt.
- Make an observing hood that your head goes under when observing. This will stop the ambient light from ruining your dark adaption when observing.
- Take off and put on your eyepatch under the observing hood to preserve your dark adaption.
Give it a go, the results are really worth the small effort.
Cheers