I passed my test, drove for 2 years (never on a motorway), then didn't drive again for over 10 years.
I avoided motorway driving until one day we were visiting friends and OH was too drunk from the night before too tired to drive. Glad I got that experience in 'cos now I have to do all the driving myself.
I would suggest doing it in stages:
Build up your confidence on dual carriageways
First time on a motorway, go early on a Sunday morning. I find it's quieter then.
You don't need to overtake at first if you don't want to. Get comfortable driving in the outside lane. Anyway, it's more fuel efficient to drive at a steady slower pace.
Once you feel comfortable and you have got used to your speed and the speed of others around you, you could try overtaking.
Once you feel comfortable doing this, you could try driving at dusk or in the dark, when people have their headlights on. I found it more difficult to judge people's speed in these conditions (hence my not agreeing with an earlier poster who said go in the late evening on your first attempt).
It took me about 3 motorway trips not to see them as something to psych myself up to doing, and about 5 to feel totally comfortable. Now, 18 months on, I don't think twice about being on the motorway and feel able to cope with all conditions.
Good luck!