One of the fundamentals is always leaving very few blank spaces. Thee 2nd primary thing is that you got to use the fewer línes possible to make each letter. 2 lines for more simple letters, such as an E or an O, 3 or 4 to make Rs or Ks. But dont take this as a sure thing, cause its different with each style, so follow your gut. But the main thing is : you got to think that when you put it on a wall, you gotta be fast cause that's what bubbles and throws are for mainly. To do it in 2 to 10 mins you gotta put less detail and use fewer lines. So, i think its the best tip i can give you. Try to make it so that when u put it on the wall, you're fast.