The Amazon Developer blog recently posted an article entitled "5 Ways to Level Up Your Alexa Skill with AWS". As the title suggests it really has extending the AWS components used by your skill in mind but the article does come up with some good suggestions to help ensure users think more highly of your skill and keep coming back.
Although following such advice will increase the AWS services that you use thus increasing the costs these ca easily be offset by the fact Amazon previously announced they would give developers $100 introductory credit for their services but they would also allow people to request more credit providing that the credit be used towards the fees generated for the skill.
The use of AWS over self-hosted skills is becoming more of a compelling argument. The need to host your own is now really being minimalised.