If the weather is good, I recommend a Capri boat tour, with or without a visit to the Blue Grotto, such as these:
There are different companies but prices are more or less the same, obviously, the more services are included in the tour, the higher the price.
[Please note, I'm a Get Your Guide affiliate: this means that if you book one of the tours through my link, I will get a small percentage of the sale (we're talking about a few euros), while the price for you will remain unchanged. This way you will help me to run my blog, without any additional expense for you. I often use Get Your Guide for my travels and have always enjoyed it].
Anyway, I always recommend reading all the details and full descriptions of the tours, what the services include and what do not, where they start from and how long they last, and also look for customer reviews. For example, I understand that the Blue Grotto is a museum and as such the ticket must be paid for at the entrance. For this reason, many of the tours do not include the ticket for the Blue Grotto in the price, it must be bought on site (the visit is, however, optional).