Despite the growing diversity of Mexico’s economy the country’s GDP still mainly depends on oil, tourism and foreign-currency remissions from Mexicans working abroad. However the opening-up of Mexico's economy is also creating a demand for experienced workers in engineering, communication and technical sectors. In particular foreign engineers with experience in specialist fields often have very good job prospects in Mexico.
If you are not a technical expert with unique experience in a specialist field, Mexico is a very challenging place to find work (especially well-paid work). Many foreigners come to Mexico rather for lifestyle reasons than for their professional career, and they are often willing to accept lower salaries and less favourable working conditions than in their home country. If you are looking for a job that seems specifically suited to foreigners (eg English teaching), be aware that you will be competing with other foreign candidates that often will accept a mere survival salary that lets them live the “Mexican experience”.
With other jobs you will be competing with Mexicans and their (often very low) salary expectations. For less-qualified positions (eg in construction etc.), you will be putting yourself at a big disadvantage if you are not willing to work long hours for a minimal salary just like thousands of Mexican workers who need to ensure the survival of their families. With more senior jobs you should not expect that your foreign qualifications are automatically regarded as a bonus in Mexico, as there are more and more highly qualified candidates leaving Mexican universities.
However there are still many Mexican companies looking for highly qualified job candidates from abroad. Foreign professionals with formal qualifications and years of experience find job-hunting in Mexico much easier than those looking for less prestigious work.
In addition to fluent Spanish a very good knowledge of another language is highly recommended. English would be of particular use, perhaps followed by another major European language such as French, German or Italian. This would work hugely in your favour especially if you are looking to work for one of the many European companies operating in Mexico.