There are several best practices for helping you improve your feedback score on eBay.
Supply plenty of information about the product & your policies: make sure to add measurements, have very clear images of the item and add your shipping and return policy in the item description.
Level of service: strive to provide the highest level of customer service, answering buyers queries on eBay within several hours. Impress your buyers with a high level of customer service.
Extra benefits: give your buyers more than expected, such as offering free shipping, fast tracking your shipping and handling time and accepting returns for a longer period of time. These are also ways to excel buyer's expectations and guarantee a positive feedback.
Send reminders: a polite message checking that the buyer is satisfied, asking them to leave feedback, can go a long way to increase your positive feedback, since also with all of the above buyers can still forget to leave feedback.
Watch the following video to learn more about best practices for increasing your positive feedback score: https://www.youtube.com/watch?v=OcVxppfWHwk