To find jobs teaching English in Germany it's best to just choose a city, and go and look, as not many schools advertise online. Check the German Yellow Pages and send out copies of your CV and cover letter to as many schools as you can. Then, after you have arrived, call the schools to remind them and see if they have any esl jobs available.
Germany has a fairly high demand for English teachers, but a lot of people looking for work, which can be difficult to find. Some people recommend the big cities, some the smaller provincial cities. The main hiring season is the end of summer, before the new term starts in September.
The bigger cities have more language schools, and probably better prospects for teaching business English, because of the larger number of companies there. However, in the smaller provincial cities there can be less competition from others who are looking for work teaching English in Germany.
Pay varies a lot, from very low to okay, but unfortunately it's not enough to save a great deal on. Some schools pay as little as €10 or €13 per hour. Others pay around €15-€22 per hour, a few pay €30-€35 per hour.
Teaching business English is more profitable. Here, earning €30-€45 per hour is possible. Some international companies have in-house training, which usually pays more than language schools.
Berlin is cheaper than the large western cities and might be a good choice, but there are a lot of English teachers looking for work there which suppresses salaries for teachers.
However, German taxes are numerous and high. Don't let this put you off if you are really interested in the country, as many people enjoy teaching English in Germany, but you need to be aware of them.
The first €8,004 is tax free. After this you will be paying from 14% up to 24% if you are earning €13,469. The taxes and charges you will have to pay include: income tax, social insurance, state pension, solidarity tax (to help fund the reunification of East and West Germany), church tax (if you declare a religion), and health insurance (I know of people paying €250+ for this one).
A degree, tefl certification , and experience are all commonly asked for. Many employers also ask for teachers who can speak German. It's a good idea to begin learning German before you arrive - if you don't already speak the language. Or start as soon as you arrive. This will also make it easier for you to arrange private classes and work in companies. Obviously, real business experience will help you find work teaching business English.
Some teachers do find work without any qualifications or experience, but this is harder and not recommended. Not recommended because you will have a higher chance of working for a low quality school, with all the problems that that entails: low salary and poor conditions generally. So the more of the above requirements you fulfill, the better.
If you are a non-EU citizen, teaching English in Germany is less difficult than in some countries. You will need a job offer and a letter from your employer.
Many teachers love living in Berlin and culturally it's rich. A quick search for groups in Berlin at Meetup.com will bring you hundreds of social, sports and other interest groups ranging from Turkish for Hipsters, and Divine Wifi Meditation to Polyglots, and Tai Chi.
The ELT market in Germany is difficult, therefore, apart from persistence, initiative, and some savings, it would help a lot if you can already speak some German when you arrive, have a business background (or at least experience teaching business and workplace English), and a CELTA. Teachers do find jobs without all of these, but they would make your life easier.