Most hand forks will require little in the way of maintenance.
However, you should clean the tines of your fork every so often with a stiff-bristled brush to remove any caked-on soil.
If your tool has a wooden handle, it should be conditioned periodically with linseed oil. Simply apply a small amount with a rag and rub in until the handle is coated with a thin layer of oil.
This will help protect and preserve the wood and prevent it from rotting so that your fork can be used for many years to come.
After use, store your hand fork, along with your other gardening tools, in a dry place such as a shed to protect it from moisture which could cause rust.