Until you are fluent, try to speak the way you write and write the way you speak, in short, simple and complete sentences.
Do not speak in a casual way and then try to write stilted or complicated prose. Even if native speakers are sloppy in their speech and use a lot of slang, as a learner you cannot afford to do so.
You don’t have a strong enough foundation in the new language. You will need to be aware of casual or slang speech in order to understand it.
But you are best to avoid it until you are quite fluent and really sure when to use it. Even though it’s hard work, writing is an excellent way to develop genuine eloquence in a new language.
If your speech is similar to your written style, each will reinforce the other. It’s less stressful to accept corrections of what you write than to have your spoken language corrected.
The corrections in your written work can then be applied to your spoken language. While spoken language is more forgiving than written language, the same phrases and words can be used effectively in both.
You should have your writing corrected regularly and your mistakes analyzed and measured.
As an example, keeping a record of the kinds of errors you make most frequently and looking for new phrases to replace the incorrect ones is one of the better ways to do so.
You can save these new phrases and compile them into a list.
Later you can create custom lists of words and phrases to use when writing and speaking. In this way you can make sure that your expression in the new language becomes richer and more accurate, incorporating the new vocabulary that you are learning.
