One of the easiest routes to working abroad is to be self-employed, although you will still need a work permit and it can be difficult to become established and make a good living. If you're an EU national or a permanent resident with a residence permit, you can work as a self-employed person or as a sole trader in a European Union country. If you want to be self-employed in a profession or trade in many countries, e.g. most European Union countries, you must meet certain legal requirements and register with the appropriate organisation, e.g. a professional must become a member of the relevant professional association. In many countries, the self-employed must have an official status and it's illegal to simply hang out a sign and start business.
Members of some professions and trades must possess recognised professional qualifications and certificates, and are usually required to take a written examination in the local language. You may also be required to attend a business administration course. You're subject to any professional codes and limitations in force, e.g. a medical practitioner must have his qualifications accepted by the medical association of the state or region where he intends to practise, and any controlling specialist bodies. You must also show that you're in good standing with the professional authorities in your home country. In certain professions, such as the law, it's unusual to be permitted to practise abroad without local qualifications.
Further information is available in our Living and Working series of books.