OH OH!!! i wana answer! lol i have been signed up (923229) for quite some time, i have never flown scince i am not big on getting the realistic feal for flying, i prefer the laid back flying we have here. I have signed up for ATC in Albequrque (hate spelling that) also known as ZAB (south west USA) Its difficult to start up in my opinion but here are some links and tips.
1. Go to vatsim.net, on the side menu there will be a selection for pilot recources, thats where you want to go.
2. I dont personally know of any pilot training cources that arnt part of a VA. British Virtual Airways has training for vastim but its a little difficult to get in (took me 3 tries at the entrance test)
3. make shure you have charts and know the airport your flying at, Controllers (in ZAB atleast) have been taught to bring aircraft out realisticly through the proper transitions
4. if you are new dont fly out of a B Class airport, the only one in ZAB is KPHX start at a small airport with a tower and feal free to ask the controller questions they usually treat the newbies rather nice. I think KABQ is a good one to start at, i havent personally controled there but its part of my training requirements.
5. Yes you can fly from a non towerd airport to a towered airport, the transition to departure is a little more difficult (peronally the departure ATC has to do more) i guess for you its going from unicom to departure, not to hard.
6. Know what the ATC is going to say so you can respond correctly, rather easy, just repeat what they say and try and do it if you understood... lol
7. now what... um... have fun!! its all about fun, after you feal comfortable i would suggest trying for ATC, its fun and it gives you the perspective all pilots should know. Its not as simple as it sounds "SWA5992 Contact Abq. center on 123.456" requres more than telling you when to switch channels. ATC needs to hand you off to the next controller and the other controller has the choice not to accep for diffrent reasons, i dont know exactly what happens but i can find out.
Have fun with it, read a little. here are some links to charts (Vatsim ATC usually expects you to have them and requires you to tell them when you dont in your flight plan)
http://www.airnav.com <-- lots of charts (PDF format)
do google searches, talk to me in Ramos' server (if i am on) name: ATC-KTUS my channel is ARTCC-KTUS
Vatsim i am 923229
Edit:
Just took a look at something i havent seen scince i joined, the reading they suggest for new pilots. well you know what i said about read a little? well scratch that... read ALOT but dont worry its good reading and will enhance your experience alot!