Both are OK. Both "okay" and "ok" are acceptable spellings in professional writing; which one you should use is merely a matter of preference (or, if you don't have one, your personal preference). In fact, only people who care about such things will even notice the difference between these two words.
When asked, "How are you?" a popular response is "good thanks" or "good thank you." You can also respond with "good thanks" or "fine thank you." After your response, it is more polite or formal to say thanks or thank you. For example, if someone asks, "How are you?" and you reply, "Good," it would be proper to follow up with "good." If someone asks you how you are and you reply "Good," they might wonder if you were actually fine. It would be appropriate to say "I'm good," and then add "thanks" or "thank you" if needed.
There are many ways to say "good" in English. One way is to use the word "good." For example, if someone asks you how you are and you reply, "Good," that would be correct. However, it would be better style to follow up with another word or two. For example, you could say "I'm good," and then finish by saying "thanks" or "thank you."
People often forget that manners matter even on social media. In order to keep your Facebook profile clean of any inappropriate content, it's best to avoid posting questions about sexual matters, drugs, and other sensitive topics. Even if you're using a fake name, people will still know you are a real person because of what you post!
If you're talking about your own words, it's usually fine, but be cautious if you're characterizing other people's words as "blah, blah, blah"! It is not used formally, yet it is often spoken. We call this language.
Use a suitable tone. A professional or business letter should be written in a somewhat more official tone than your ordinary language. Avoid slang or jargon, contractions like "I'm," "can't," and "it's," and imprecise terms like "good" and "nice." Even if you are grumbling, be nice and considerate. Your recipient will feel important when you address him or her by name.
Structure it correctly. The first thing to do is to decide how you want the letter to look. Will it be typed or handwritten? If it is going to be typed, then use a typewriter rather than a computer keyboard for best results. When writing by hand, make sure you have good handwriting; otherwise, your letter will come across as unprofessional.
Include all the necessary information. You should include your own contact details at the beginning of the letter so that your recipient does not have to search for them. Make sure to include a copy of your identification document (such as a driver's license) as well.
Be concise but informative. Use simple language and avoid long sentences. Try not to repeat yourself- keep it short and sweet! - and include only the necessary information. If you think of something else important to say, you can always add a footnote or endnote later.
Follow up. Once you have sent your letter, it is important to follow up with a phone call or an email.