When messaging with a colleague, only use abbreviations or Internet slang that you would be comfortable saying out loud. Only use emojis if you are certain your colleague will understand your message. Think of an emoji the same way as abbreviations - if you wouldn't wear the emoji on a T-shirt to work, don't use it in professional communication.
Whether you are using Skype for Business, Facebook, or Gchat, be mindful of a contact's status. If a contact's status is Busy, think about contacting them later or send a brief email if your question is time sensitive.
Respond to messages in a timely manner. Utilize status features such as Busy and Away to let others know how to best contact you. Be consistent with the resource you use to message so others know where to find you and what to expect out of engaging with you.
If you need to go beyond 160 characters, write an email or make a phone call instead.