Speak English
The requirements for teaching English in China are quite clear however there is some room for variation. This is mainly based upon the company you are applying to and the location. The key requirement is to be able to speak English. This does not mean to say you must be a native English speaker although, of course, this is much preferred. English, American ,Canadian South African and Australian are typically the most common nationalities but if you have an English oral proficiency as a second language that can be accepted. Some companies favour English natives and others Americans and dialects are not usually an issue unless perhaps it is a particularly harsh one.
Degree
A degree. This can be in any subject and therefore pretty much just confirms the holders level of professionalism. It was possible to have a graduate qualification equivalent however to get the expert certificate required to teach a degree is the key. I do know of people who have had a certificate issued to them with a HNC however this was during 2013 and has now stopped. Some companies are willing to forge qualifications however this should raise alarm bells in your head if this is mentioned, after all how reputable can a company be if they suggest it?
Contract
A job contract is ideal as you will definitely need a letter of invitation from a company and if a company is inviting you to work for them then you are likely to have a contract! Not many people are going to fly half way around the world on a say so and not have one! A Invitation letter will be issued by your employer and sent to your postal address. This must be an original and not a photocopy so expect either a four week delay or a 200RMB DHL charge. Contract copies are usually done via email and not required for your visa application. You will be expected to forward your qualifications in advance so electronic copies are a good idea.
TEFL/CELTA/DELTA/TESOL
A TEFL certificate (Use code Buddy 360021311 for discount) or equivalent is also a must. Some people choose online courses that issue qualifications based upon the amount of study hours invested whilst others do CELTA/DELTA or TESOL diplomas. If you decide upon an online TEFL then do a minimum of 120 hours. This is considered an advanced level and therefore more worthy. Any additional practical courses are usually welcomed. Some companies offer TEFL training however most will almost certainly offer induction training. This is especially useful if you have never done this before.
Experience
There is some discussions regarding the requirement of mandatory prior experience. I have not seen any evidence of this as yet and therefore consider this a subjective matter. Once again a lot depends upon your employer, whether it be an agency or directly with a school and the location. Either or, this will not effect your Visa application. This is discussed above and therefore does not need repeating.
Z Visa
Your Z visa is a working permit that expires upon arrival. It allows you thirty days to enter China and must immediately be exchanged for a residency permit. This will involve having probably two interviews with the local authorities that your FAO (Foreign Affairs Officer) will arrange. The topic is mostly why you are here and what you will be doing to which your FAO will/may answer for you. Sometimes you will not even be expected to speak, just show your face! The expert certificate is also something your FAO will arrange once you have your visa and in the country.
Travel Insurance
You must have travel insurance and provide a copy of your policy. There are many online companies that cover this and some specialise in just China. These are usually cheaper. Get it before you leave although you can get covered directly online and only takes a few minutes to complete an application. A clean CRB check is required so if you have any convictions you had better fess up in advance. I wouldn't worry about three points on your licence for speeding this will not matter. It may actually go in your favour in this country (Joke).
Medical
Health Medical. This can be fun! China is very strict about your general health and condition when entering the country and you may/will get temperature checked at the border. This is NOT invasive but just either a hand held scanner or a full body scan. This is a bit like a standing CT/MRI type scan. A full medical will then be required and involves the following. Urine and blood samples, chest Xray, ECG, abdomen squeeze, eye sight and hearing check, weight and height measurements, blood pressure, boob feel (Girls) and reflex check. The Chinese are quite efficient at doing this and you can expect to take about half a day for it. Note: be prepared for a potentially upsetting set of results if you find out something you didn't know before! It has happened.
The last and final thing you are definitely going to need is a large set of balls! It takes courage and a sense of adventure to do it but it does work and the rewards are many. A number of personal things have not been covered here such as money and clothing etc but this should give you a fair insight into what to plan and what to expect upon arrival.