In order to get a thicker branch on a bonsai fig it would mean getting the branch to grow faster and have more leaves than other branches on the tree. Another way is to fuse several branches together to achieve greater thickness.
The easiest way to propagate most Ficus trees is to use cuttings. Cuttings of any size Ficus generally will root. However, some people prefer to use an air-layering process as this can be a safer way to propagate a specific piece.
One interesting thing to know is that Ficus leaves can vary greatly. They can vary in size, shape, texture, color etc. They even can vary on the same plant or whether the plant is growing strongly or just slowly.
Growing figs from seed reveals also that almost every seedling shows some subtle or not so subtle variations. The picture below shows two leaves grown from a Thailand seed source and the other from an Australian source. They are both the same species, Ficus virens, Lipstick fig, Red Balete, Spotted fig are all common local names for them.
The two leaves really do not look similar and yet they are the same species! Makes me scratch my head trying to ID figs from across the world by just looking at the leaf. For a true identification the syconia or figs need to be seen. Unfortunately, we seldom see figs on our bonsai.
To learn more about growing figs buy the definitive reference work on Ficus for bonsai. The book is a softcover, 8 by 10 inch volume, with 144 color pages, containing detailed information for the beginner as well as the advanced hobbyist. Click here for more information
An uncommonly found Ficus species, Ficus glumosa is from Africa and has nice round, hairy leaves. It is in the grouping of rock-splitter figs. Those that seem to be found growing over and around rocks in the veldt.
Since they seem to enjoy rock growing this seedling was placed over the rock to emulate a root over rock style. It is in a small pot so its growth is quite limited and despite its age, about 12 years, it is still a very immature bonsai design.
One of the best small leaf fig species to use for bonsai is the Willow Leaf fig, scientifically called Ficus salicaria. It has many great features including aerial roots and wide-spreading surface roots. One possible issue is that it does not like having roots that stay too wet. Water the tree well and make sure to allow the soil to nearly dry before watering it again. Continually wet roots leave room for fungal and other rot problems.
Ficus carica, the edible fig, is grown throughout the world for its delicious sweet figs. It prefers growing in climate areas that have some sort of resting season, either from cooler winter temperatures or a dry season. I have tried growing it in a tropical greenhouse without a proper cool or dry period and found that it does not grow well for me under these conditions.
For interest I am showing a few specimens that I saw growing out of rock walls during a recent trip to Greece.
Bunjin or literati style is a less common bonsai style. It mainly relies on the line of the tree for its focal point. The canopy and the pot should be minimal to keep the focus on the line of the tree. It is a style that has its admirers as well as many that do not like it. I have a short article at http://www.bonsaihunk.us/info/Bunjin_literati_Style.html
One thing that I find very useful is to photograph my trees on a regular basis. This allows me to see how the trees progress over time and lets me photographically change the images to see if a better design emerges from the image manipulations.
A series of pictures to illustrate how the design might change after playing with image manipulations.