Minimize first messages that are vague, such as "Hi" or "Have a minute?". Instead, state your idea, question, etc.
Favor shortcuts such as symbols, hashtags, emojis, etc. Example: "+1" means "I agree", "#todo" means "For our TODO list", and a green-checkmark emoji means "Done".
Prefer using topic channels over direct messaging, because topic channels can help more people, in more ways, over more timelines.
Lift important information from chat and messaging into a better long-term place, such as a wiki, or documentation page, or
Be explicit about expectations. Example: if you expect chat and messaging to be interrupt-driven, or 24x7 urgent, or response-required, then write it.
If you want information to be available to the teammates, then emphasize all-team channels versus one-to-one channels.
Ensure people get responses. If people feel that channel messages are not getting adequate repsponses, then people tend to go back to DMs and other high-escalation communications.