I've had a lot of ideas when thinking about more ways to teach players than just the manual some weeks ago. They were are also intended to get players to join public rooms instead of private, passworded ones, so the actual playerbase grows.
All these ideas require newbies to understand that the systems are very helpful and that using them is highly recommended.
1) Mentor systemExperienced players should be able to mentor new players. Give them a little form where they can choose how many nubs they'd like to mentor. When players start ZKL the first five or so times they are asked whether they'd like to have a personal mentor. Tell them that they are free to ask mentors any question and that they can abandon a mentor at any time.
Then pick a mentor based on some simple algorithm: Mentors that speak the same language (country flag) come first, if none exist then mentor with most free capacity (in percent) is picked, if same then higher elo mentor is picked.
2) Dedicated newbie channelForce newbies into a channel while they are level 1-10, tell them that they are free to ask any question there. Ask the community to help out where possible. Use it to organize newbie-rooms where experienced players spectate or play in a nubs team and guide them.
3) Live streamed tutorialsThis is probably more of an event-based idea. I doubt players are willing to stream tutorials 24/7. These can probably organized and announced in the channel mentioned above.
The idea is to provide a video stream of experienced players participating in real battles to give new players a serious game to look at. Newbies should be able to see exactly what the player sees: Mouse movement, camera position, etc. It'd be awesome if there was an overlay that displays which keys are currently pressed. Newbies should be able to ask the player either through a chat or via mumble what exactly (eg how he plopped a marker, etc) he did or why he did it when they see something confusing.
Out of those the dedicated newbie channel is probably the easiest thing to implement. I'm not sure how the live-stream could be solved. The stream would need to have a high resolution so newbies can see the mouse. The game has to run with very high fps. Both at once is hard to achieve and requires a good internet connection from streamers and newbies.
On previous posts: I don't think singleplayer content will be of much use. I've often read that most players who play SP games never play MP.