What's the best way to increase the trunk size and reduce the leaf size on a ficus that I rescued from the wild. The tree has definitley grown in the year since owning it, with a notable difference in the nebari, however the trunk is only 1cm in diameter with the biggest leaves reaching 15cm in length. Im not quite sure if I should prune back now that its come into Spring and if so where and how much? I have fertilised once with Seasol liquid fertiliser as well as some slow release pellets. Is there another type of fertiliser I can use which would help to thicken the trunk?

Hamo1180 wrote: What's the best way to increase the trunk size and reduce the leaf size on a ficus that I rescued from the wild

Let it grow to increase the trunk. This tree will not be ready for leaf size reduction for the next years.

notable difference in the nebari

It's OK to simply call it roots. Nebari is a term for something different.

Why the pebbles?

Sorry, I thought the Nebari referred to the very low knuckle part of the trunk. So, should I not even prune back every second new leaf? What about fertilising?
And the pebbles are just for show. Would that cause the pot to contain TOO much moisture and in turn cause root rot?

Hamo1180 wrote: Sorry, I thought the Nebari referred to the very low knuckle part of the trunk

It refers to a flare of surface roots. At this stage you cannot talk about Nebari yet.

So, should I not even prune back every second new leaf?

Nope. It's too young and too small to be pruned at this stage.

What about fertilising?

Yes please. Follow the instructions on your fertilizer product.

And the pebbles are just for show. Would that cause the pot to contain TOO much moisture and in turn cause root rot?

It will prevent you from properly seeing when the plant needs water. On bonsai, it's not done, as it doesn't look good.
Only cheap wholesale 'bonsai' have pebbles.

it looks like you have the bonsai bug, incurable!
firstly bonsai really need to be outside, have you been trying to grow this inside with the light in the background? Low light will produce large leaves as these are the factory of the tree, and low light will cause the tree to grow larger leaves. if the area you are in is to cold to grow figs choose another species. If it is a tropical region, then put your tree, outside in a black squat pot with good soil. Prefferably put it on an area of the ground that thee roots will grow from the bottom of the pot into the ground. it will explode with growth once this has happened. Be sure to wire your trees trunk prior, and keep a check that the wire isnt cutting in.
Unfortunately putting a tree in a pot doesnt make it a bonsai! If you are serious you will take the long road and do it properly, (there is no short road). Join a local bonsai club, listen, learn and above all enjoy the journey!
Here is an old ficus nerifolia shohin of mine that has done the years.