Some suggestions:
1) give them problems not drawn to scale to force them to have to redraw the figure. The act of redrawing helps to give a better understanding of the problem and demonstrates how important having a good picture is
2) give them diagrams with many intersecting lines and have an activity to see who find the most number of polygons amongst the lines. This will help them to "see through the mess" and pick out different shapes. Once they get the hang of this give them similar diagrams except with a few angles given and have them find the missing angles, again looking for shapes and line patterns they recognize
3) introduce them to various forms of geometric art (islamic tile design, tessellations, isometric drawing, perspective drawing etc) to give them a context to why drawing shapes can be fun/important
4) literally practice drawing shapes based off of a description (ex: "Draw a square with sides 4 inches", "Draw a triangle with sides 3, 5, 7 inches", "draw quadrilateral QUAD") some of your students may just have no experience with drawing, especially geometric shapes, so good old fashion practice might help them to get more comfortable
5) give them problems that "require" drawing a picture, i.e. it is very hard to reason about the problem without drawing a picture. The Discovering Geometry textbook has a lot of good problems where drawing a picture is crucial
6) model drawing a diagram for a student when working through a problem with them (ex: "so the way that I thought about this problem was to draw a picture, what do you think my picture looked like?")
These are all things I have done with my Geometry class and while they do not always draw a picture, they have definitely been drawing them more often since the beginning of the school year, hope this helps