It is an outside bonsai and prefers full sun, but in very sunny areas part shadow is better. Young trees need some shelter in midsummer. Give plenty of water during the growing season.
Protect well against frost, for the Ginkgo is very sensitive for it in shallow pots because of the fleshy roots with moistury content that might burst open with frost. Therefore keep it fairly dry in winter. 
A bonsai needs to be more fertilized than a normal sized tree. Fertilize plentiful with organic manure: spring-October twice per month. 
A female branch may be grafted on the tree to get seeds earlier than normal. 

It does not need (much) wiring. Just prune the branches which are too long so that its form keeps  in balance.
The bark is delicate, so be careful; if you apply wire do it lightly and use aluminium wire.
Protect the bark with raffia and check regularly.
 

Repotting
Young trees (up to about 10 years) need to be repotted every year in early spring just before the leaves appear. Older trees may be repotted every 2-3 years or only when necessary. Use basic soil mix that is well-drained, add 10% coarse sand and some grid. Do not prune the roots too much in the beginning.
 
 
 

In Japan many of the Ginkgos of over 100 years old or older produce aerial chichi. In Japan they are called “chichi icho" = chichi Ginkgo (chichi means nipple or breast), in China "zhong-ru" (meaning stalactite). Such trees can provide propagation material to grow a Ginkgo chichi bonsai. Female trees with large aerial chichi usually get no seeds.

Air-layering of relatively large branches from a chichi Ginkgo is the best method to get a chichi bonsai. This will result in a large plant within 3 years. Grafted or rooted plants take many years to form aerial chichi.

Girdling the trunk of a Ginkgo seedling with wire or bark ringing stimulates the forming of a chichi-like structure above the girdle.

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An old Chinese legend:

It is said that when Emperor Kao Tsung moved from Kaifeng in the north to Nanking and Hangchow in the south in 1127, the imperial cavalcade crossed the Yangtze River into southern Kiangsu. Coming to a town called Chen I, near the city Kunshan between Soochow and Shanghai, an official named Kung I, a native of the northern capital Kaifeng, picked a branch of a Ginkgo, stuck it into the ground and prayed that if the branch lived, he would settle there. 
The branch later developed into a huge tree and in later years the trunk became gnarled and twisted and adorned with many hanging ‘nipples’ as in other venerable trees of the same kind.

'This penjing created by an artist of the Sichuan School displays a highly unusual shape. The trunk resembles stalactite, a mineral formed through limestone corrosion. No human effort could possibly sculpture this kind of bole. 
In nature, Ginkgo trees of several hundred or even over a thousand years of age frequently develop a host of stalactite-shaped substances which suspend from the trunk. If these are removed in winter and planted upside down, an incredible thing will happen – foliage will sprout off the ‘stalactite’. The branches can later be wired. 
A penjing of unique style, known as ‘Stalactite Trunk’ or ‘Bamboo Shoot Ginkgo’ will result.'

* More about Ginkgo chichi bonsai in: Del Tredici P, Ginkgo chichi in nature, legend & cultivation, International Bonsai - 25, no.4, 1993.