Lettering is all about drawing letters, instead of just writing them the way you usually do - without thinking!
If you want to add some words to something you've drawn, then it's really important that you think of the letters as part of the design, because they sure are! One way is to make the words part of the central image, instead of adding them somewhere in the background. Like in the image above - there's plenty of room to fit "Merry Christmas!" in the snow below the gingerbread house, but I made it part of the smoke instead. Now the viewer has the nice surprise of discovering a cheery message somewhat hidden in the smoke.
This image is one of 31 Merry Christmas! designs I drew last December, drawn in black marker and colored in Photoshop or Illustrator.