1. Do NOT try to make all the food yourself; let others get involved. Try to find out what your guests prefer to bring; some enjoy making creative desserts while others like the simplicity of bringing bags of chips. Personally, I provide the main dish and one side dish when hosting a piano party. This way, if someone isn't able to attend the party at the last minute, you have the necessary food for a meal.
2. Have plenty of drinks (i.e. water, lemonade, soda, and fruit juice). This is especially important if you are hosting your party outside. During our summer piano party, there is drink table outside with a 5 gallon water cooler and a cooler underneath the table with fruit drinks and small water bottles. Later, I'll usually bring out a couple 2-liters (root beer, lemonade, etc.) for the meal.
3. Choose easy recipes you can make ahead of time. By choosing easy recipes, the food prep on the day of the party should be minimal. As an example, I make macaroni salad the night before, and right before the guests arrive, I place hotdogs in the crockpot.
4. Include at least one music-themed food item. This is a nice touch and will reinforce the "music" theme of your party. Check out my Pinterest board Recital Recipes featured below for some fun creative ideas.