Study languages that are most useful to the position you want. Want to lead tours in Italy? Learn Italian. Does your company have a large international clientele? Learning French, German and Russian may be useful. The more languages you speak, the easier it will be to find a job.
Travel. If you are seeking work with a tour company, having traveled is essential. It is best if you have traveled to some of the places they travel.
Try to get experience leading tours. Leading tours of your hometown can be a good stepping stone to leading more substantial tours.
Don't expect getting a job with an international tour company to be quick or easy. Keep in mind that languages are a huge asset, and many Europeans are raised speaking three or more. Additionally, remember that competition is steep. Persistence and preparation are key to finding a job with an international tour company.