Hello and welcome to the forum. As a relative beginner myself, there are others who will be able to provide a wealth of advice but I will will give you a few ideas to start with.

First, a couple of questions. What camera are you using and what are its capabilities?

For deep space photography, (galaxies, nebulae...), you are gathering light so, in general, the longer the exposure, the greater the depth and colour. So you are stacking fewer long exposures.

For lunar or planetary you are taking lots, ie. hundreds of shots, choosing the best and stacking these to overcome atmospheric interference and enhance features.

For stacking I use registax which is a free download. It handles avi files best so if you are already using a ccd camera it will work well. If you a using a digital camera, the jpeg files need to be stacked manually, ( there is a tick box for this ). To select the shots you want to stack, create a separate file containing only the shots you have chosen to stack.

Open registax and then use the select option to select the files. You will then need to align the shots by selecting one or more alignment points, (prominent features in the frame with reasonable contrast). Once chosen, assuming the alignment features are in a similar position on each frame, registax will proceed on its own. Registax may ask you to select the feature manually on each frame. I have found the selection of alignment points to be more art than science but others may be able to offer some tips here. When finished, select 'Limit', (which controls the quality of the stacked image by limiting pixel differences), and then 'Optimise and Stack'.

Registax will stack automatically. You will then be presented with a battery of powerful image processing tools for limiting noise, enhancing selected wavelengths... At this stage I save the stacked image as a bitmap and then reopen it in photoshop cs2 for processing as I find the tools in photoshop simpler to use. I will eventually bite the bullet and learn how to use some of the histogram and wavelet filtering devices.

Thats enough to start with so good luck and enjoy. I hope others wiil chime in with other ideas for you.

Kind regards
Matt