Do this practice test will help you with a lot of questions: https://www.udemy.com/aws-certified-developer-professional-2018-practice-exam-test/learn/v4/content
Also this site is giving some good hints: https://wiki2.easycloudsolutions.com/display/AC/2017+Exam+Questions%3A+AWS+DevOps+Professional
Do the SampleExam questions: https://d1.awsstatic.com/training-and-certification/docs/AWS_certified_DevOps_Engineer_Professional_SampleExam.pdf
My Sample questions answer: C D B B B B B B C C
Read the Service description page with all the feautures for all the services you are not familiar with.
Read the FAQ.
Follow an official AWS Training if possible
You can add AWS Elastic Beanstalk configuration files (.ebextensions) to your web application’s source code to configure your environment and customize the AWS resources that it contains. Configuration files are YAML- or JSON-formatted documents with a .config file extension that you place in a folder named .ebextensions and deploy in your application source bundle.
We recommend using YAML for your configuration files, because it’s more readable than JSON. YAML supports comments, multi-line commands, several alternatives for using quotes, and more. However, you can make any configuration change in Elastic Beanstalk configuration files identically using either YAML or JSON.