This is silly answer.
If you want to make new players stay in game, you sit and think how to make new players have fun. (This you can do for other people, too)
Only, "This game is very boring. If you don't like being bored, go away" means you lose all new players and game dies.
If only fun thing is war then find ways for more war. I think this is why players come.
After, you teach them the other fun things that are slow.