Might help some get a list of things in the mind to check for certain basic situations. At worst if you can get the easy stuff spot on you have more minors to save for the tricky/unexoected stuff!!
The fact you’re in a relatively big vehicle doesn’t alter what’s happening on the road. But your reactions have to be tuned to deal with the situations bearing in mind the vehicle you’re in.
If, for instance, you’re approaching a roundabout on a fast motorbike, you would be ill-advised to enter the roundabout if another vehicle would have to slow down. Indeed, this would be suicide. Exactly the same principle applies if you’re in a car, truck, bus, tractor; enter the roundabout if no-one will be hindered as a result. Don’t enter if this isn’t the case.
As ROG said, a car going straight ahead at a roundabout will often straight line the roundabout. This means he can maintain a higher speed - something you must allow for before going for it.
I hate relating stuff just to passing/failing a test. But, in this particular case, I’ll relent. Few folks fail a test for hesitation. You would have to sit and eat your sarnies before it’s gonna happen. But all to many fail because they think they’re under pressure to make progress. This results in folks pulling out when they shouldn’t - - and often know very well they shouldn’t. This will always attract a serious mark for observation. The pressure is not to make progress, it is to make SAFE progress. And pulling onto roundabouts and slowing anyone down isn’t safe.
Whilst on the subject, a pet hate of mine is the trainee blaming folks for not signalling on a roundabout. So what? If someone hasn’t got a signal on, this means they are going straight ahead ie across your front bumper. Therefore, don’t go. Now if they turn off at the junction before yours without a signal, shame. No mark will be made against you on a test. Why would it? Conversely, if someone has their left signal on before they get to the exit before yours and then fails to leave the roundabout, it’s possible you could move out slowing them down and not attract any mark. But if their position and/or speed give it away as potentially an incorrect signal, then an examiner would be correct in marking a serious for observation. So if someone’s on the roundabout, belting round, and have their left signal on for a smallish exit, I wouldn’t pull out. And no mark for hesitation would be given btw.
The same basic principles of proper driving apply to all classes of vehicle. Just adapt them to the size of your vehicle bearing in mind it’s acceleration and braking characteristics.
Hope this helps, Pete 
Nailed the reverse with one wee shunt, nice enough drive then as I pulled out onto a roundabout in the right gear and position on approach (fully commited) there was only one black saloon car approaching the roundabout from the right, he was waaaaaay back from the give way lines as I pulled out, but must have been hammering it (well above the 30mph speed limit) he scorched onto the roundabout, got right up my back end and started honking his horn 
)