If you want to use your 3D printer as a plotter, you need to somehow mount a pen. Here are 4 things to consider...
Your 3D printer is fairly accurate, but a pen mount can introduce error. For the drawing to turn out well (with crisp lines and no wiggles) you'll need the pen to follow the printer's movements as precisely as possible. This means you need the pen to be mounted securely in place.
Your printer's bed (probably) isn't perfectly flat. It helps to have a spring-loaded pen mount that allows the pen to move freely in the vertical direction. That way the pen stays in contact with the paper in locations where your bed sags, and the pen retracts (instead of breaking) where your bed peaks. The vertical movement should be smooth, and shouldn't introduce any play in the X or Y directions.
In order to maximize your drawing area, you'll want the pen to be mounted near your printer's nozzle. If your printer has a bed area of 300mm x 300mm, and your pen mount has a 30mm x 30mm offset from your nozzle, you'll only be able to plot on 270mm x 270mm. Having a mount that requires you to remove the extruder is less convenient but it typically gives you more plot area.
Most mounts have a maximum pen diameter.
With these points in mind, we've tested several of the mounts posted on thingiverse. Our favorite to date is: Thing: 3365530. It clips into the fan vent, and uses rubber bands to create a spring-loaded effect. It's a little finicky to adjust the pen height, and there's a little play in the X & Y directions, but overall it works pretty well for getting started.
If you want to match the precision of what is being produced on PlotterTwitter with drawing robots like the axidraw ($475 for the lowest end model), you should check out the mount we designed - it's available now. It attaches quickly and securely to the stock Creality fan shroud. And with very little play it lets you get consistent high quality drawings from your 3D printer.