I can go kinda slow in traffic already, but find myself wobbling the handlebars quite a bit - guessing this is cos I dont use the clutch properly?
Not so much...
More like you're focussing on one thing, whereas it's a combination of rear brake, clutch-feathering and a bit of throttle, as well as balance and keeping the bars steady, while trying not to either blast into the vehicle in front or delay the one behind, as well as trying to keep pace with the vehicle in front that is almost certainly riding the clutch and creeping casually along instead of just going up to where it needs to be and stopping solid...
Plus it's a 125 and likely weighs nothing!
Would it be worth practicing on my little bike like IC3 said? - I can see the benefits for sure, but just how different is it all on a "big bike"?
In many ways, VERY different.
I found I developed 125 habits that did not work on a big bike.
The bigger is usually easier as the weight helps to plant it well, both in slow manoeuvres and in leaned-over cornering.
However, the clutch is easier to feel, but can also be harder to control and balance with the throttle. You'll be used to your own clutch anyway, but bigger bike means more power, especially if you dump the clutch or something.
Better to have some time on the school bike, as you'll have to use the big one for the test anyway. Get as used to that as you can. You'll also have the benefit of the instructor's eye.
How exactly do you go slow and controlled then?
Revs up a *little*, rear brake off and gently let the clutch out just enough for it to get the bike moving. Hold the clutch at that point and very lightly use the rear brake only to control the speed.
Holding the clutch here, you should be able to rev the **** out of the bike and it won't pick up speed at all. However, this is just something instructors do to demonstrate, NOT something you should aim for on the test.
It's then a case of maintaining this controlled state and your balance, looking where you want to go and actively driving the bike round... ideally at walking pace.
Would you expect me to need any more that a day or so training on a big bike?
Depends what bad habits you've picked up.
Observation is KING on motorcycles and seeing things as early as possible will give you time to plan for them and set up ready to negotiate them.
This is FAR better than reacting to them.
Therefore, your checks are the best thing to work on - Most examiners can tell if you're actually looking correctly, or just turning your head and pretending.
Mirrors are cool - Look in them often. Every 15-ish seconds, if only to make sure you don't have a car up your bum. Check one, look back to the road and then check the other.
Signals - Know when the right time is to use these - Too early, or too late - to avoid confusing other vehicles, as well as remembering to cancel them just after you complete the manoeuvre.
Position - A small one in most peoples' minds, but which will come into play as you learn how to control your road space. Staying dominant during normal riding is fairly easy, but moving to one side before turning and the like discourages vehicles from going around you and is often safer.
Speed - Be aware of how fast you're going. You can get away with nudging over the limit, but only for a few seconds here and there. Go massively over or remain above for any length of time and you may well fail.
Try and keep it about 3-5mph under the limit. So in a 30mph limit, you want to be between 25 and 30.
Also pay attention to the limits of the current road - 30s are easy, 40s just as much. Your instructor will likely take you down the NSL roads the examiner will use, but really watch for any 20 limits. If you're not sure, err on the side of caution and watch the side roads - These often have speed limits posted, because that's where they change, so if you're in a "may be 20, may be 30" and are passing a 30 sign, chances are you're in a 20.
Look - Lifesavers are called that for a reason.
