Within the European Union
European nationals do not need to apply for visas for EU member states. Depending on the duration and nature of your stay, you might however be required to report to immigration police after arrival and apply for a residence permit.
Outside of the European Union
Start early with arranging your visa. The rules and regulations for applying for a visa differs for each country. You can obtain more information from the relevant country’s embassy or consulate. See website below for more information.