Paint all your colors to color pops, or daisy-s. This can help to not open every nail polish, or colored gels, during the choose. Also, clients can see the colours better in this way.
Tip: separate them by tones. Dark and browns, pinks and cyclamens, reds and burgundies, funny colours...
Paint nail polishes just the same way as on the clients (2 layers of colour, 1 layer top coat). Never try to fix the problems (strokes, light colour...) of the nail polish. Your clients will be dissapointed at differences in results.
Tip: every three month, use fresh layer of top coat, to protect the colours, and bring always fresh, bright effects.
Paint different frenches. Simple french, french with different tips, pink base, beige base, french designs, so clients can easily choose from a variation of ideas.
Tip: paint only that desingns, what you can do perfectly.