There are a lot of various simple nail ideas to recreate for your next appointment. But here I think I can suggest you a few options to consider. For example, think about stripes, if you want to them yourself it would be possible to use tape or a nail art striping brush to create straight lines in different colors.

The classy option are french tips, you can think about doing them colorful or combine with other design elements.
Glitter gradient is also very creative type of simple design. Paint your nails a solid color and then use a makeup sponge to apply glitter polish to the tips.
If you want to combine few colors in your manicure, you can try ombre nails.Paint your nails a light color and then use a makeup sponge to apply a darker shade to the tips, gradually blending the colors together.