Peruse the PCF Chip DB, the ChipGuide, and various threads here showing off some great designs. I recommend you just explore and see what speaks to you- colors, spots, inlay elements. Do you like simple or complex? Vintage or modern? What color combinations do you like? Some great stuff that can really help inspire. Take note of what you like and don’t like. Take your time and let your tastes develop.
Get samples. There are multiple OEM chip vendors, plus resale vendors, plus folks here. You can buy your own new customs, vintage, used casino, used customs, used chips and replace the inlay…. Do you like high end plastics, cheap ceramics, expensive ceramics, clay? Minty with hard edges or broken in buttery? Having chips in hand and seeing them makes a huge difference.
Once you have a direction, start your engines. If you’re buying existing chips, start shopping and looking. If you’re going custom, you can hire a designer or do it yourself. I did a set in PowerPoint, another in Inkscape, and another in Curve (fka Vectornator). There are other options as well, including Adobe Illustrator.
How you go depends on you, what you like, and your budget.