Hi Kym! I also like to paint the odd space scene, and generally use acrylics, as this system offers the brightest colour when you need them.
I usually tackle a space scene as I would any subject; by studying the light and colours and composition.
I've spoken with David A Hardy, who is a superb space artist, and he often uses acrylics, but he also uses fine spray techniques to achieve brilliant lighting on planets.
A spatter brush (SAA) is very useful to achieve scattered and realistic star fields, and some knowledge of Astronomy will be really useful.
My advice would be to look at some existing work (google David A Hardy) and study some of his work, noting his use of colour and light to show an almost 3D effect against a very dark background.
Then have a go yourself, and try to achieve a good result.
Think of it this way; a space scene is simply a landscape somewhere else!!
Have a go, and if you want to explore the subject a little deeper, then come back to me and I'll do my best to help.
Very best wishes and good luck!
PA / RSC Wigan / Warrington / St Helens