Plan the object before opening Blender
Measure the cable and choose where the clip will sit. Sketch a simple base and an opening for the cable. Choose approximate dimensions and leave enough material around the opening. The first version is a prototype; expect to adjust it after a test print.
Build from simple shapes
Start with a cube for the base. Set its dimensions deliberately. Add a second shape to define the cable channel and use a Boolean difference to cut it. Keep the result simple, then add a modest bevel to edges that should feel less sharp. Save your Blender project as you go.
Check before export
Make sure the channel is open and large enough for the cable. Inspect the mesh and its real dimensions. Confirm that the base and walls are substantial enough for your printer. If you are unsure, use the printability checklist.
Export, slice, and test
Export the printable object as an STL, then open it in your slicer. Check the layer preview and choose an orientation that gives the clip a stable base. Print one test piece. See whether the cable fits and whether the clip holds up in use.
Improve the next version
Change one thing at a time: opening width, wall thickness, corner radius, or mounting method. This is the useful loop: idea, model, print, improve. For more context on the full workflow, read the beginner's guide to Blender for 3D printing.