Several options to make it easier for new players to find the commands they need:

1) /Help command for a list of most popular commands in alphabetical order
2) Let's say you use /gamemode, but type an invalid one, the message should give an array of possible gamemodes to choose from
3) perhaps autocompletion for the commands

Thoughts?

/gamemode supports many more possible values in 5.12, including abbreviations, so hopefully you'll type one that's allowed.

I'm not sure what you mean by autocompletion: is that different from what happens when you press tab now?

when you press tab when in chat you have "/gamemo" it'll be "/gamemode", but if you press tab in chat when you have "/gamemode si" you don't get "/gamemode singleplayer" or other options like it