There are hundreds of settings that can be placed in my.cnf. For the 'lite' user of MySQL, they won't matter as much.
Once your database becomes non-trivial, it is advisable to set the following parameters:
This should be set to about 70% of available RAM (if you have at least 4GB of RAM; a smaller percentage if you have a tiny VM or antique machine). The setting controls the amount of cache used by the InnoDB ENGINE. Hence, it is very important for performance of InnoDB.