1. Make sure your nails are clean of dirt, oils, and any old nail polish before applying a new polish.
2. Use a base coat to help the polish last longer, and to prevent staining of the nails.
3. Use a top coat to seal the colour and prevent chipping.
4. Consider the brand/quality of your nail polish. Some polishes chip more quickly, whereas others will last for a very long time (does not necessarily mean the more expensive ones are always better...many drugstore brands have great staying power!)