My instructor had me driving on a dual carriageway on my second lesson. Given that it was the A14 (which is effectively an extension of the M6 and carries thousands of container lorries heading to the countries largest port, Felixstowe), I think that he must have had a death wish!
Just a few hints for you:
1. When entering a dual carriageway from a slip road, it's really important to match your speed to that of the traffic in the near-side lane, sop that you can simply slip into a gap.
2. Even so, remember that other drivers aren't obliged to make space for you. 'Matching your speed' might, for example, mean doing 60mph but you still need to be able to stop at the end of the slip road if no gap appears!
3. (I know it's stating the obvious but . . . ) keep your distance from the vehicle in front at ALL times. When passing a slow moving lorry, for example, many drivers get right up behind it before pulling out, rather than pulling out at least 15 car lengths behind it (which good driving practice requires). Similarly, if a queue of overtaking traffic forms when you're in the outside lane, still keep well back from the vehicle in front of you. (For some strange reason, many drivers who would never 'tailgate' in the nearside lane seem to regard it as normal practice in the outside lane!)
Good luck!