Vocabulary

• Teaching requires a higher level of language than is used on the street. To adjust to this, you will need to have a sense of which words are high language and which are not. Building your sentences with a combination of the two will almost certainly lead to distraction, and amusement. (Eg. “Subsequent to the reconciling exchange to reinstate Peter, Jesus says that some dudes will someday take him out.”) For those teaching with a translator, choose simple words that the translator is sure to know.
• We also must learn to fit our language to our audience. We all know that in English, the way you communicate something to a teenager is different than how you do so to an elderly woman. So too in other languages.

Grammar

• It's not about keeping the rules, but saying it naturally.
• Therefore we must not only learn vocabulary, but also learn to switch the order of our sentences. This is critical, unless we want to sound like Yoda and turn people's attention to our strange constructions. For those teaching with a translator, this also is important to understand. For the translator might not be able to translate a half sentence at a time. You may need to give him/her the whole thing since he/she will start the sentence where you ended it.
• Thus, when teaching with a translator, we do best to use short, less complex sentences. If we are learning the language, on the other hand, we need to observe how long of sentences locals typically form and try to do likewise. For example, in German a sentence is an essay, whereas in Modern Hebrew it is three clauses at most. 
• The connections made between sentences can also vary significantly between languages. Does the language like participles? Does logic tend to be signified through explicit conjunctions or emphasis and ordering?

Pronunciation

• The goal is not accentlessness—the goal is understandability. Accents are interesting...so long as you can understand the person without strain. Thus, we should get a sense of how easy or difficult we are to understand when we teach in a place that has not always been our home.
• If it means going to a speech therapist (as it did for me) to figure out how to say a certain sound, it is worth it. We must speak in a way that people can understand.

Idioms

• The first order of business related to idioms is to become aware of your English idioms! Often, we do not even take notice when we use common idioms, but will need to do so if we want to communicate in another language without confusion. For those speaking with a translator, this simply means avoiding idioms as much as possible. If you do not, your translator will surely stumble in his/her translation. For those learning a second language, this means checking which idioms translate. Some will. Many won't. And it is easy for your teaching to get completely side-tracked by using a non-existent idiom. (Can you spot the three English idioms used within this bullet point?)
• In terms of local idioms, try them out in everyday conversations far before you insert them into a teaching. You need to know them inside and out before you brave them from a podium.
• But also understand that you cannot obsess about precision. Idioms often don't have prefect logic behind them. They are defined by usage and so need to be heard and used a lot for them to become our own.

Make the hard choices to learn language well

1. Live where English is not spoken. Major city centers and particular neighborhoods with English-speaking populations will be easier for you to adjust to a new culture. It will reduce the stress... but it will not help you with language. If you and your family can bear the difficulty, live where you have no choice but to use the local language.
2. Speak the local language at home too. Certainly you will make many mistakes that are not caught by your family members who are also learning, but the value of the practice far outweighs this. For my family, we chose one day per week where we would only speak in the local language. When that was no longer overwhelming, we bumped it up to two. And so on we continued up to six days per week.
3. “Grow-up” on television. A great way to knock out two birds with one stone is to watch baby and children's television. It both presents language at your level and gives you priceless shared experience with nationals through the songs and shows you will learn.
4. Seek correction. Ask friends to always correct you and “reward” them with tons of appreciation when they do. Write out your teachings in the local language and have them reviewed by a person who will not be afraid to use his/her red pen. Better, read them aloud to the person to see how emphasis and pronunciation can be improved as well.
5. Get a job in the local language. It will likely not be your preferred job and probably won't pay all the bills, but it will do more for your language than formal language classes can.
6. Make space. We all know that children learn language far faster than adults. While I do not doubt that the state of our brains is a factor in this, I would suggest that the biggest difference is time of exposure. Many children go to school all day long in the local language. Then we adults resign to the fact that we could never learn language so fast and so well. Certainly, we won't if we are unwilling to give it so much time!
7. Decide to be a fool. This is the biggest factor that will decide the success or failure of your language learning. Are you willing to look dumb? If not, you will never open your mouth. Kids care little if they mess up the grammar and vocabulary and so they just go for it, and their language takes off.