welcome newbie
firstly, have you done any painting and decorating work outside of the college?, reason being, normally the college only shows you the basic sides of decorating, you have to work with actual decorators and do a varity of jobs.
if you have done that and feel fairly confident thats fair enough, me personally,have done 3 years with a big building company, left it for a while to have kids, then went back to it, but did some work for firms and building sites, then went on my own (self employed)
the beauty of working with decorators, I mean the proper ones lol, is that you learn so much from them, more than any college will teach you.
Just work out how much you want per day, or what the going rate is in your area, work out how much you would have to pay out on your stamps, tax, holiday, public liabilty insurance etc,then add it all up and thats what you charge plus materials.
It may pay you to get some leaflets made up, I do it once every 18 months or so,, and I go out and put them thru letterboxes, you could offer a discount to begin with to work up your client base, after a while it will be word of mouth, but it can dry up the odd time, thats why it pays to keep your hand in with the leaflets.
or advertise in the newspaper, yellow pages etc, or put cards up in shop windows.
Explain on your advert what you can actually do, ie paperhanging, interior work or exterior work, free estimates, no job too small and all that.
Good luck