My sculpting skills are not very good – so my advice is only worth as much as you’re paying for it.
However, the basics of using greenstuff – or any similar epoxy putty – are reasonably straightforward.
You don’t really need to buy lots of fancy tools, as a cocktail stick will suffice for most purposes; but if you want to develop your skills a bit, then the following are helpful:
The KY jelly is to lubricate your…sculpting tools.
You can just use water, but it tends to flood the putty easily. Some people use Vaseline or olive oil instead – but these are liable to affect the adhesion of paint; whereas a water-based lubricant can be washed-off easily.
Which turns into green stuff when you’ve kneaded it together:
If the putty is new, it’s best to wait 15-20 minutes after kneading it together, before you start sculpting; otherwise it tends not to retain its shape. If it’s old, you shouldn’t need to wait.
I usually keep sculpting work simple, as when it goes wrong it can look a bit duff; but it is often necessary to plug gaps. So, it’s worth learning how to use greenstuff properly.
It was mainly needed for a bit of repair work here, but also to add some detail. You can see the damaged plastic around the shoulder area:
Smooth it down – shaping it to match the surrounding contours:
It was much the same with the left side of the model:
Organic shapes are fairly easy, and are a good place to start if you’re new to sculpting. Straight edges require a bit more precision to look right:
I think the key is just practice – to be patient, and build layers up gradually. Confidence also makes a difference, too – but don’t be afraid to remove the putty and start over again, if it goes wrong.